Custom Solar & PV Infrastructure Gaskets, Pads & Insulators
H-O Products die-cuts and converts UV- and ozone-resistant EPDM foam, closed-cell silicone sponge, solid-silicone grommets, ePTFE vent membranes, polyimide dielectric film, UHMW-PE and PTFE wear strip, thermally conductive interface pads, and edge-protection foams into the enclosure gaskets, junction-box and connector seals, module-frame edge protection, tracker wear pads, rooftop isolation pads, and inverter thermal interfaces that keep photovoltaic balance-of-system (BOS) hardware weather-tight, cushioned, and insulated across a 25-year field life, built to your drawing.
Built for: string/combiner-box and recombiner enclosure sealing, string- and central-inverter enclosure seals and thermal interface pads, module junction-box and connector seals, module-frame edge protection and glass setting blocks, single-axis tracker bearing and wear pads, and rooftop mounting isolation, on hardware built toward an IEC 60529 IP or NEMA 250 Type target.
To spec the soft goods for photovoltaic (PV) balance-of-system hardware, choose the family from the hardware and the failure mode. For a combiner-box, recombiner, or inverter enclosure door built toward IEC 60529 IP65/IP66 or NEMA 250 Type 4/4X, specify EPDM closed-cell foam for UV and ozone exposure, or step up to UL 94 V-0 closed-cell silicone sponge (HT closed-cell class) for desert / rooftop temperature extremes, a flame class, or coastal salt.
The remaining zones and duties are mapped in the When-to-spec list on this page. Values are per the TDS on file; see the material reference below for ordering details.
By designation (belongs to the complete enclosure or module): IEC 60529 (IP ingress-protection code) · NEMA 250 (enclosure Type designations 3R/4/4X) · UL 50 / UL 50E (enclosures, environmental) · IEC 62790 (junction boxes for PV modules) · IEC 62852 (PV DC connectors).
Material-level, per the maker TDS: ASTM D1056 (flexible cellular rubber) · ASTM D2240 (durometer) · ASTM D1149 (ozone cracking) · ASTM G154 (fluorescent-UV weathering) · ASTM D395 (compression set) · ASTM B117 (salt-spray / fog) · ASTM D5470 (thermal impedance of TIMs) · UL 94 (flammability classes, incl. V-0).
- Combiner / inverter door, UV / ozone: EPDM foam
- Door + desert temp / flame / salt: HT closed-cell-class silicone sponge or V-0 FR silicone sponge
- J-box / connector seal: solid silicone + polyimide film
- Breathing enclosure / condensation: ePTFE vent membrane
- Tracker bearing / wear: UHMW-PE / PTFE wear strip
- Module-frame edge / setting block: XLPE / EPE foam
- Rooftop mounting isolation: EPDM / felt protection pad
- Inverter thermal path: BN-silicone TIM pad
This guide is for solar EPC, balance-of-system, and PV-hardware engineers and procurement teams specifying enclosure gaskets, junction-box and connector seals, module-frame edge protection and setting blocks, tracker bearing and wear pads, rooftop mounting isolation, and inverter thermal interface pads for utility-scale, commercial-rooftop, and distributed PV, on hardware built toward an IEC 60529 IP or NEMA 250 Type target and a 25-year field life.
Where are you in the spec process?
This page serves PV engineers who already know the part they want and engineers still working out the spec from the hardware and the failure mode. Pick the path that matches where you are; you don't have to read the rest.
Send a drawing, get a quote
An EPDM or silicone enclosure gasket, a solid-silicone grommet, an ePTFE vent membrane, a UHMW-PE tracker wear pad, module-frame edge protection, a thermal interface pad, or a complete BOS soft-goods kit on your drawing.
Skip to the quote form →Walk through material selection
Six selection factors (outdoor duty, UV/ozone durability, temperature window, flame & salt, compression & wear, entries & breathing), a BOS-hardware material selector, and eight material families with TDS-cited grades and test methods.
Start with selection factors →
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1Send drawingUpload a DXF, STEP, or PDF, or describe the enclosure, the junction box, the tracker bearing, the module frame, or the rooftop foot. A sample part works too.
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2Material reviewEngineering reviews the IEC 60529 IP or NEMA 250 Type target against the vendor TDS, checks compression range, temperature window (desert / rooftop extremes), UV/ozone durability, flame and salt exposure, tracker wear duty, and whether a vent membrane is needed. The rating is framed correctly: it belongs to the complete enclosure, and the material carries its own classes by TDS.
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3PrototypeSamples typically ship in 3–5 business days for common configurations on materials we keep on hand. Made-to-order; MOQ varies by material and part.
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4ProductionStandard production runs ship about 2 weeks after drawing approval, including kiss-cut-on-liner and PSA-laminated configurations. Expedited service available. Ongoing parts run with material traceability and lot-code TDS records.
PV hardware → outdoor duty & failure mode → material selection → converted part → production supply.
- 1PV hardwareName the hardware: combiner / inverter enclosure, junction box, module frame, tracker, or rooftop foot.
- 2Outdoor duty & failure modeSet the IP / NEMA target and the failure mode: ingress, UV/ozone, thermal-cycle breathing, wear, or heat.
- 3Select material familyEPDM foam, silicone sponge, solid silicone, ePTFE vent, UHMW-PE / PTFE, polyimide, TIM pad, or edge foam.
- 4Add adhesive / liner / profilePSA backing, kiss-cut-on-liner, or a specific cross-section from the drawing.
- 5Die-cut to drawingPerimeter gasket, grommet, vent disc, wear pad, edge channel, or setting block cut to your geometry.
- 6Quote prototype or productionSamples, first article, and production supply with lot-code TDS records.
Which PV hardware are you building for?
Application Zones
Seven hardware families define the soft goods of a PV balance-of-system: the combiner and inverter enclosures, the module junction boxes and connectors, the module frame, the single-axis tracker, the rooftop mounting, and the breather that keeps every sealed box from condensing water inside. Each has one controlling failure mode and a matching converted part. Click a tab to see the hardware, the controlling properties, and the families H-O converts for it.
Combiner & inverter enclosures: the field-mounted door seal
The hinged door or bolted lid of a string combiner box, recombiner, or string / central inverter is the enclosure's worst joint, and its perimeter gasket is what earns the outdoor rating in the field over a 25-year plant life. The default is EPDM closed-cell foam: UV-, ozone-, and weather-stable (UV weathering per ASTM G154, ozone resistance per ASTM D1149), with compression-deflection classes per ASTM D1056, economical for the long runs a door perimeter needs.
Where the site runs to desert or rooftop temperature extremes, calls a flame rating, or sees coastal salt, step up to closed-cell silicone sponge (HT closed-cell class), which the maker TDS rates roughly −55 to 200 °C with a UL 94 V-0 class and low compression set. The controlling number over decades is compression set, not the day-one seal, which is why silicone earns its premium on the harshest field enclosures.
In North America the NEMA Type designations are listed in the UL 50 / UL 50E enclosure environment, cited here by designation. [2] The full outdoor-enclosure gasket playbook lives on the outdoor-power sibling page; this zone is its PV-BOS edition.
Inverter sealing & thermal: the enclosure seal and the interface pad
A string or central inverter is two problems in one box. First, the enclosure seal: the inverter self-heats under load and cools when clouds pass or rain hits, so its door and gland-plate gaskets take the same UV/ozone and thermal-cycle duty as a combiner, sealed with EPDM foam or, for the widest temperature window and any flame class, silicone sponge.
Second, the thermal path: the inverter's power stages interface to heat sinks through electrically insulating boron-nitride silicone thermal interface pads and soft gap-filler pads, whose thermal impedance is reported per ASTM D5470 at a stated pressure on the TDS. The deep TIM and EMI selection logic lives on the power-systems thermal-management and EMI-shielding sibling pages; this zone points to the parts H-O converts for the inverter, and frames the honest rule: the IP/NEMA rating belongs to the complete enclosure.
Module junction boxes & connectors: the distributed leak path
Every module carries a junction box and a pair of DC connectors, so the J-box and connector seal is a leak path repeated across thousands of modules in a plant, the definition of a distributed reliability problem. The junction box is governed at the component level by IEC 62790 (safety requirements and tests to 1500 V DC, including dielectric, thermal-cycling, humidity-freeze, and UV) and the DC connectors by IEC 62852 (with UL 6703 the US counterpart); PV junction boxes typically reach IP67/IP68 with silicone potting.
What H-O converts is the soft-goods around that hardware: solid-silicone grommets and gland seals sized to the cable and wall (durometer per ASTM D2240, holding a low compression set through the outdoor temperature swing), and, where a design calls a dielectric layer, a polyimide film barrier. H-O supplies the converted seals and insulators; the junction-box and connector safety evaluations belong to those tested components, not to a part.
Module-frame edge protection & setting blocks: cushion and locate the glass
A glass PV laminate set hard against an aluminum frame concentrates stress at the contact line and cracks under wind uplift, snow load, and thermal expansion mismatch over the years. The fix cushions and locates the glass: an crosslinked polyethylene (XLPE) or expanded-polyethylene (EPE) edge-protection channel runs the laminate perimeter, and setting blocks locate the glass and carry the bearing load at defined points.
Where the frame joint also needs a weather seal, a closed-cell EPDM foam strip carries it with UV/ozone stability. These are conversion parts, cut and profiled to the module drawing; the module qualification (its IEC 61215 / 61730 testing) belongs to the module maker, and H-O supplies the cushioning and protection inside that design.
Single-axis tracker bearings & wear pads: 25 years, maintenance-free
A single-axis tracker rotates its torque tube through millions of slow cycles over a 25-year plant life, on bearings that have to stay maintenance-free, no field re-greasing, no seizing, and low-friction under wind and gravity loads. The answer is a self-lubricating polymer wear surface: UHMW-PE wear strip (ultra-high-molecular-weight polyethylene, with a coefficient of friction in the PTFE class and high abrasion resistance) and virgin skived PTFE or PTFE-coated fiberglass where the lowest friction or a thin slip layer is needed.
Both are UV-stable and run dry, which is exactly what a field bearing needs. H-O the wear pads, bushing strip, and slip washers to the bearing and pillow-block geometry; send the bearing detail, the load, and the rotation duty.
Rooftop mounting isolation & protection: separate racking from the roof
On a commercial-rooftop PV system the racking feet and ballast blocks sit on a finished roof membrane, and bare metal on membrane abrades, punctures, or thermally bridges it over the years.
The fix is an isolation and protection pad between the racking and the roof: a closed-cell EPDM foam or slip pad that cushions the foot and blocks abrasion (UV/ozone stable where exposed), a pressed-felt protection pad under ballast blocks to distribute the point load and protect the membrane, and, where a slip interface is wanted for thermal-expansion movement, a PTFE slip layer.
H-O the protection pads and slip sheets to the foot and ballast-block footprint; the roof-warranty and attachment design belong to the roofing and racking system.
Breathing & vent: the condensation fix a gasket alone cannot make
A fully sealed PV enclosure has a hidden failure mode: over the daily temperature cycle, amplified by load self-heating and sudden rain-cooling, the internal air pressure rises and falls, drawing humid air past even a good gasket and condensing water on cold interior electronics, a fuse block or a control board. The seal did its job and the box still got wet.
The fix is a ePTFE vent membrane: an expanded-PTFE microporous film that passes air and water vapor to equalize pressure while blocking liquid water, dust, and salt, so a combiner, recombiner, inverter, or monitoring enclosure breathes without losing its IP or NEMA rating. It is the layer most PV enclosure specs omit and most field-condensation complaints need. Pair it with the door gasket; together they keep the interior dry across the thermal cycle.
Six decisions that drive your PV balance-of-system material spec
A PV balance-of-system part is a single-purpose piece with one controlling property per job. Miss one and the failure is rarely immediate: a gasket relaxes below its sealing force over years, a UV-crazed run opens a path, a sealed box condenses water inside, or a tracker bearing wears through.
Materials carry classes; enclosures and modules carry ratings. A UL 94 V-0 class belongs to a material grade per its TDS. An IEC 60529 IP66 or NEMA 250 Type 4X rating belongs to the complete tested enclosure, and a module's IEC 61215 / 61730 qualification belongs to the module. Write material classes on the part callouts, cite enclosure and module standards by designation, and never let a drawing imply a gasket is "IP66 rated": the gasket supports an enclosure evaluated to it.
Tip: put the material class on the part and the enclosure rating on the assembly note.
Utility PV plants are engineered for a 25-year outdoor life, so the controlling material numbers are the ones that erode slowly: compression set and stress relaxation on the seals, UV and ozone durability on every outdoor elastomer, and wear rate on the tracker bearings. A material chosen for day-one performance and not for the decade is a spec that quietly expires in the field.
Read the six factors below in order. The first sets the outdoor duty; the next three read the environment (UV/ozone, temperature, flame and salt); the fifth sizes compression and wear; the sixth closes the entries and adds the breather. Every factor names its test method, because on a 25-year plant the documentation is part of the part.
Show all 6 selection factors tap to expand
Outdoor duty: start from the IP / NEMA target and the hardware
Rule — the outdoor duty drives everything downstream. An IEC 60529 IP65 combiner (dust-tight, low-pressure jets) is a different job than an IP66 inverter (powerful jets) or an IP67/IP68 potted junction box; the NEMA 250 Type 3R/4/4X designations are the North American counterparts. The rating is earned at the complete-enclosure level, but it sets the gasket's compression class, chemistry, and geometry. Name the IP code or NEMA Type and the hardware on the drawing; the material family follows from it. [3]
UV & ozone durability: 25 years outdoors rules out commodity elastomers
Rule — over a 25-year field life, chemistry beats price. UV and atmospheric ozone surface-craze standard neoprene and SBR within a few seasons, so the PV-outdoor default is EPDM (UV- and ozone-stable; UV weathering per ASTM G154, ozone per ASTM D1149) or silicone. Confirm the part sees direct sun before defaulting to neoprene; reserve neoprene for shaded or bolted joints. The UV-weathering and ozone data on the TDS are what separate a material that lasts the plant life from one that crazes. [5]
Temperature window: EPDM to ~150 C, silicone to ~200 C for desert & rooftop
Rule — the thermal swing picks the chemistry. EPDM covers the ordinary outdoor range to roughly the 120–150 °C class; a desert site, a rooftop-mounted inverter, or a high day/night swing that needs a wider window steps up to closed-cell silicone sponge, rated roughly −55 to 200 °C per the HT closed-cell-class TDS. State the low and high service temperatures; the maker TDS ranges are only meaningful against the actual desert or rooftop duty, and heat aging is what erodes recovery on the hot side. [11]
Flame & salt: the two step-ups that pick silicone
Rule — a required flame class or a coastal salt exposure moves the choice to silicone. Where a combiner or inverter gasket must carry a UL 94 V-0 class, specify V-0 FR silicone sponge or an HT closed-cell-class V-0 silicone sponge (class per the grade TDS). Where the site is coastal, marine, or de-icing-salt exposed and the enclosure is a Type 4X, favor silicone over EPDM for salt resistance (salt exposure per ASTM B117 at the enclosure level).
Call the flame class and the salt exposure explicitly; let them pick the track before cost does. [9]
Compression & wear: size the seal to closure force, the pad to the wear duty
Rule — two mechanical jobs, two numbers. For a seal, match the compression-deflection class (per ASTM D1056) to the real closure force and watch compression set (per ASTM D395) over the 25-year life. For a tracker or slip interface, the controlling numbers are coefficient of friction and wear rate: UHMW-PE and PTFE run dry and maintenance-free. Send the closure force and gap for seals, and the load and rotation duty for wear pads; the grade falls out of those numbers. [8]
Entries & breathing: close the penetrations and let the box breathe
Rule — the spec is incomplete until the entries and the breather are drawn. Cable, conduit, junction-box, and connector penetrations are the distributed leak path: seal them with solid-silicone grommets and, where called, a polyimide dielectric barrier. And any sealed PV box that cycles daily will breathe, so add a ePTFE vent membrane to equalize pressure and stop internal condensation. List the entry sizes and whether the enclosure is fully sealed; a fully sealed box almost always needs the vent. [14]
Specification Tools
Two tools to take you from "we're building a PV balance-of-system part" to here's the material family and what to send: a hardware-and-duty selector that maps your PV hardware and failure mode to a material family with its citation language, and a side-by-side comparison of every PV-BOS family on this page.
1. PV balance-of-system material selector
Pick the PV hardware and the controlling duty. The selector returns the default material family, what to send with the drawing, and the citation language (material classes per TDS; enclosure and module ratings by designation, held by the complete assembly). Every family is also printed in the material reference section below, so nothing here exists only behind a script.
Recommended family: EPDM closed-cell foam
For a combiner or inverter enclosure with a UV/ozone weather duty, EPDM closed-cell foam is the UV- and ozone-resistant default. The IP/NEMA rating is held by the complete enclosure; the material carries its own compression class per ASTM D1056, UV weathering per ASTM G154, and ozone rating per ASTM D1149 on the TDS.
2. Side-by-side: PV balance-of-system family comparison matrix
Every family called out on this page, with construction, the class that drives its selection, the standards its TDS cites, and the hardware it serves. Click a column header to sort. Click any material name to jump to its accordion entry.
| Material | Construction | Selection class | Standards on the TDS / by designation | Hardware | |
|---|---|---|---|---|---|
| Enclosure & entry sealing | |||||
| EPDM Closed-Cell FoamOzone / UV-stable foam | Closed-cell EPDM foam | UV / ozone default | ASTM D1056; G154; D1149 | Enclosure doors, roof pads | |
| Closed-Cell Silicone Sponge (HT closed-cell class)Wide-temp / V-0 | Closed-cell silicone foam | Temp / flame / salt step-up | UL 94 V-0; ASTM D1056; D395 (TDS) | Desert / salt enclosures | |
| V-0 FR Silicone SpongeFlame-rated sponge | Closed-cell FR silicone | Flame class on gasket | UL 94 V-0 (per TDS) | Flame-rated enclosures | |
| Solid Silicone RubberGrommets / entry seals | Solid silicone, ~30–80 Shore A | Durometer / interference | ASTM D2240; D395 (TDS) | J-box, connector, cable | |
| Dielectric, breathing, wear, thermal & module | |||||
| Polyimide Dielectric FilmThin insulating barrier | Polyimide film | Dielectric barrier | IEC 62790 context; dielectric per TDS | Junction boxes | |
| ePTFE Vent MembraneBreather disc | Microporous ePTFE film | Pressure equalization | Passes air/vapor, blocks water | Breathing enclosures | |
| UHMW-PE / PTFE Wear StripSelf-lubricating | UHMW-PE / skived PTFE | Friction / wear rate | Maintenance-free, UV-stable (TDS) | Tracker bearings, slip | |
| BN-Silicone Thermal Interface PadInsulating TIM | Boron-nitride silicone pad | Thermal impedance @ pressure | ASTM D5470 (per TDS) | Inverter power stages | |
| XLPE / EPE Edge ProtectionCushion / setting block | Closed-cell PE foam | Cushion / bearing load | ASTM D1056 (per TDS) | Module frame, roof pads | |
Skip ahead and request your BOS materials review now
If your drawing set already calls out an EPDM or silicone grade, a grommet, a vent membrane, a UHMW-PE wear pad, an edge-protection profile, or a thermal interface pad, send it over for review against the TDSs and the enclosure- and module-rating language.
PV balance-of-system material failures you can prevent at spec
PV balance-of-system hardware fails quietly first: a gasket that relaxed below its sealing force, a UV-crazed run, a sealed box that condensed water inside, a tracker bearing that wore through, a module frame that cracked its glass. Five patterns cover most of what goes wrong across a 25-year plant, and each is a specification decision made before the first part is cut.
On a PV plant, the rating you shipped is not the rating you keep. UV, ozone, salt, and 25 years of daily thermal cycling erode a gasket's sealing force and a bearing's wear surface long after the day-one IP / NEMA test passed. Specify for the decade, not the demo: low compression set, UV/ozone-stable chemistry, maintenance-free wear pads, and a breather where the box will cycle.
Show all 5 failure modes tap to expand
1. The enclosure gasket relaxed, and the rating quietly expired
Fix — a combiner or inverter door gasket picked by gap fill seals on day one and relaxes forever. As years of daily desert or rooftop thermal cycling take a compression set, the contact force drops below the seal threshold and the enclosure loses its IP / NEMA rating without any visible failure.
Specify the force window, not the gauge: match the compression-deflection class (per ASTM D1056) to the real closure force, and choose a low-compression-set chemistry, silicone sponge holds recovery widest across temperature (compression set per ASTM D395).
The family's compression-set resistance is what keeps the spec alive over the plant life. [8]
2. UV and ozone crazed a commodity gasket over the plant life
Fix — a standard neoprene or SBR gasket put in direct outdoor exposure surface-cracks under 25 years of UV and ozone, and the cracks open a leak path. The failure is chemistry, not geometry. Use the UV/ozone-stable outdoor chemistries: EPDM or silicone, with the UV-weathering data (per ASTM G154) and ozone rating (per ASTM D1149) confirmed on the TDS. Reserve neoprene for shaded or bolted joints where it is not taking direct sun. [5]
3. The sealed box got wet inside because nothing let it breathe
Fix — a fully sealed combiner or inverter enclosure with a perfect door gasket still condenses water inside: the daily temperature cycle, amplified by load self-heating and rain-cooling, pumps the internal air pressure up and down, drawing humid air past the seal, and the moisture condenses on cold interior electronics. The seal did its job; the box still failed. Add a ePTFE vent membrane that equalizes pressure while blocking liquid water and dust, so the enclosure breathes without losing its rating. [14]
4. The tracker bearing wore through and the drive stalled
Fix — a single-axis tracker bearing surface picked wrong wears through over millions of slow cycles, gains friction, and stalls or over-loads the drive, and re-greasing a field of trackers is a maintenance line nobody wants. The fix is a self-lubricating polymer wear surface that runs dry for the plant life: UHMW-PE wear strip at a coefficient of friction in the PTFE class, or a PTFE slip layer where the lowest friction is needed. Both are UV-stable and maintenance-free. Send the bearing geometry, the load, and the rotation duty. [13]
5. The module frame set hard on the glass and cracked it
Fix — a glass laminate set directly against the aluminum frame concentrates stress at the contact line and cracks under wind uplift, snow load, or thermal expansion mismatch. The fix cushions and locates the glass: die-cut crosslinked-polyethylene edge protection around the laminate perimeter and setting blocks that carry the bearing load at defined points. Match the foam's compression class (per ASTM D1056) to the load and keep the cushion continuous where the glass meets the frame. [6]
Material reference
Detailed specs for the eight PV balance-of-system families referenced on this page: the enclosure and entry sealing set (EPDM foam, closed-cell silicone sponge, V-0 FR silicone sponge, solid silicone), the dielectric and breathing layers (polyimide film, ePTFE vent membrane), the tracker and module set (UHMW-PE / PTFE wear strip, XLPE / EPE edge protection), and the inverter thermal path (BN-silicone interface pads).
Values are per the maker TDS on file for each grade with the method named; enclosure and module ratings are cited by designation only, with the rating held by the complete assembly. H-O die-cuts, kiss-cuts, slits, and kits every family to drawing.
EPDM Closed-Cell FoamBOS-door default · UV / ozone stable · ASTM D1056 classes, G154 UV, D1149 ozone
Specify the compression-deflection class to the real closure force, and confirm the UV-weathering and ozone data on the grade TDS. The full outdoor-enclosure gasket playbook is the outdoor-power-substation-sealing sibling page.
Closed-Cell Silicone Sponge (HT closed-cell class)Desert / rooftop / salt step-up · −55 to 200 °C, UL 94 V-0 per TDS
HT closed-cell-class silicone foam is a standard outdoor-enclosure gasket for dust, moisture, and wind-driven rain per the maker TDS. Specify the V-0 grade where the location calls a flame class on the gasket.
Flame-Resistant V-0 Silicone SpongeFlame-rated closed-cell silicone · UL 94 V-0 per TDS
The flame class belongs to the grade per its TDS, not to the enclosure. Pair it with the enclosure's own rating language.
Solid Silicone RubberJ-box / connector grommets & entry seals · ~30–80 Shore A · ASTM D2240
Getting the durometer and interference right is the whole job; send the cable outer diameters and the wall detail. The junction-box (IEC 62790) and connector (IEC 62852) evaluations belong to those components.
Polyimide Dielectric FilmThin insulating barrier · junction boxes & connectors · dielectric per TDS
H-O supplies the converted dielectric layer and its TDS; the junction-box and connector safety evaluations (IEC 62790 / IEC 62852) belong to those tested components, not to a film.
ePTFE Vent MembraneBreather disc · pressure equalization · passes air/vapor, blocks water
A fully sealed PV box almost always needs the vent; it is the layer most enclosure specs omit and most field-condensation complaints need.
UHMW-PE & PTFE Wear StripTracker bearing & slip pads · self-lubricating · maintenance-free, UV-stable
Send the bearing geometry, the load, and the rotation duty; the friction and wear numbers come off the grade TDS. UHMW-PE and PTFE are the maintenance-free, dry-running wear chemistries.
Edge Protection Foam (XLPE / EPE) & Inverter TIM PadsModule-frame cushion / setting blocks & inverter thermal path · ASTM D1056 / D5470
Match the foam's compression class to the load per ASTM D1056, and state the real mounting pressure for a TIM pad, because the ASTM D5470 impedance on the TDS is only meaningful at the pressure the assembly applies.
SAE Pressed Felt (F-1–F-55) + Cork Pads (Plain MS113, Rubberized)Compliant liners, strike pads, leveling, anti-slip · ASTM D461 felt methods · F36 cork compressibility
None of these parts carries serious load; all are dimension-critical, which is exactly what die-cutting is for.
Coated Acrylic Foam Tape (AFTC)Structural bonding & brackets · gap fill, tolerance take-up, stress relief
Solar PV balance-of-system materials: engineer-grade FAQ
Twelve of the questions we hear most from solar EPC, balance-of-system, and PV-hardware teams. If your question isn't here, send a drawing or call, engineering picks up.
Is a gasket "IP66 rated" or "NEMA 4X rated"?
No, and no honest supplier claims otherwise: IEC 60529 IP codes (IP54, IP65, IP66) and NEMA 250 Type ratings (3R, 4, 4X) are earned by the complete tested enclosure, not by a gasket. The dust, water, and salt-spray tests are run on the assembled box. What the gasket carries is its own material documentation: compression classes per ASTM D1056, UV weathering per ASTM G154, ozone resistance per ASTM D1149, a UL 94 flame class on the rated grades, and lot-code traceability.
The gasket supports an enclosure evaluated to the rating; H-O supplies the converted part and the TDS, and the enclosure designer owns the rating. [3]
EPDM or silicone for a combiner-box or inverter door?
EPDM closed-cell foam is the economical PV-outdoor default: UV-, ozone-, and weather-stable, covering the ordinary outdoor temperature range with compression classes per ASTM D1056 (UV weathering per ASTM G154).
Move to closed-cell silicone sponge (HT closed-cell class) when a desert or rooftop site pushes a wider temperature window (roughly −55 to 200 °C per TDS), a UL 94 V-0 flame class, or coastal salt exposure, silicone holds its recovery widest across temperature and resists salt better. Match either one's compression class to the real closure force. [11]
My sealed PV enclosure still gets condensation inside. Why, and what fixes it?
Because a fully sealed box breathes: over the daily temperature cycle, amplified by load self-heating and sudden rain-cooling, the internal air heats and cools, building pressure that draws humid air past even a good gasket, and the moisture condenses on cold interior electronics. The seal did its job; the box still got wet. The fix is a ePTFE vent membrane, an expanded-PTFE microporous film that passes air and vapor to equalize pressure while blocking liquid water and dust, so the enclosure breathes without losing its IP or NEMA rating. [14]
What gasket goes on a coastal or desert PV enclosure?
At a coastal or marine site the target is usually a NEMA 250 Type 4X (or IEC IP66) enclosure, and the gasket choice favors silicone over EPDM for salt resistance; the enclosure earns the 4X by design and the extra 200-hour salt-spray exposure (apparatus per ASTM B117). At a desert site the driver is the wide day/night temperature swing, which also favors closed-cell silicone sponge for its −55 to 200 °C window and low compression set.
Either way pair the gasket with a vent membrane, because the daily thermal swing makes these field boxes breathe. [9]
How do I seal a PV module junction box and its connectors?
The junction box is a component governed by IEC 62790 (safety requirements and tests to 1500 V DC, incl. dielectric, thermal-cycling, humidity-freeze, and UV) and the DC connectors by IEC 62852 (UL 6703 in the US); PV J-boxes commonly reach IP67/IP68 with silicone potting. What H-O converts is the soft goods around that hardware: a solid-silicone grommet or gland seal sized to the cable outer diameter and wall (durometer per ASTM D2240), and a polyimide dielectric barrier where the design calls one.
H-O supplies the seals and insulators and their TDS; the component safety evaluations belong to the tested J-box and connector. [4]
What material goes on a single-axis tracker bearing?
A self-lubricating polymer wear surface that runs dry for the 25-year plant life. UHMW-PE (ultra-high-molecular-weight polyethylene) wear strip has a coefficient of friction in the PTFE class with high abrasion resistance, and virgin skived PTFE or PTFE-coated fiberglass gives the lowest friction where a thin slip layer is needed.
Both are UV-stable and maintenance-free, no field re-greasing, which is exactly what a tracker bearing across acres of field needs. H-O the wear pads, bushing strip, and slip washers to the bearing and pillow-block geometry; send the load and the rotation duty. [13]
What cushions a glass module in its frame?
Die-cut edge protection and setting blocks. A glass laminate set hard against the aluminum frame concentrates stress and cracks under wind uplift, snow load, and thermal expansion mismatch. A crosslinked-polyethylene (XLPE) or expanded-polyethylene (EPE) edge-protection channel runs the laminate perimeter to cushion it, and setting blocks locate the glass and carry the bearing load at defined points, with compression classes per ASTM D1056.
The module qualification (IEC 61215 / 61730) belongs to the module maker; H-O supplies the cushioning inside that design. [6]
How do I protect a rooftop membrane under PV racking?
An isolation and protection pad between the racking foot or ballast block and the roof. Bare metal on a membrane abrades, punctures, or thermally bridges it over the years, so a closed-cell EPDM foam or slip pad cushions the foot and blocks abrasion (UV/ozone stable where exposed), a pressed-felt pad under ballast blocks distributes the point load, and a PTFE slip layer lets a foot move under thermal expansion without abrading.
H-O the pads and slip sheets to the foot footprint; the roof-warranty and attachment design belong to the roofing and racking system.
What thermal interface pad goes in a PV inverter?
An electrically insulating, thermally conductive pad between the inverter's power stages and its heat sinks: a boron-nitride silicone interface pad, or a soft gap-filler pad where the gap varies and low mounting pressure is needed. The controlling number is thermal impedance, reported per ASTM D5470 at a stated pressure on the TDS, so state the real mounting pressure because the datasheet curve is only meaningful there.
The full inverter TIM selection logic, including gap-fill versus thin-bond-line trade-offs, lives on the power-systems-thermal-management sibling page. [12]
Why did my PV enclosure gasket lose its seal over several years?
Compression set. A gasket picked by gap fill seals on day one and takes a permanent set over 25 years of daily thermal cycling; once its contact force falls below the seal threshold, the enclosure quietly loses its rating with no visible failure.
The defense is to specify the compression-force window rather than the thickness, pick a low-compression-set chemistry (silicone holds recovery widest across temperature), and size the compression mid-range so recovery is left. Compression set is tested per ASTM D395 for solids and per ASTM D1056 methods for cellular grades. [8]
Can H-O kit the full BOS soft-goods set for a project?
Yes: the enclosure door and gland gaskets, the entry grommets and dielectric barriers, the vent-membrane discs, the tracker wear pads, the module-frame edge protection and setting blocks, and the inverter thermal interface pads can ship as a kitted set, one kit per enclosure or per tracker row, parts on liner in assembly order, with lot-code TDS records per material.
That is exactly the documentation a quality or field team wants, and it removes the field guesswork of matching the right part to the right joint. Send the enclosure or tracker drawing and the part list.
Does H-O extrude the door seal profile, or it?
H-O and converts sheet, roll, and blanket stock to drawing: die-cut and kiss-cut perimeter gaskets, grommets, vent discs, wear pads, edge-protection channels, setting blocks, and thermal interface pads. Extrusion is not one of our in-house processes; extruded profiles are coordinated through a partner network with their own tooling lead times. Conversion runs in Winsted, Connecticut under an ISO 9001:2015 certified quality management system with material traceability and lot-code TDS records. Send the drawing and we frame the manufacturable option.
Glossary: terms used on this page
Quick reference for the balance-of-system, enclosure-rating, and outdoor-durability terminology used throughout. Each entry links to the relevant standard or test method where applicable.
Balance of system (BOS)
Everything in a photovoltaic plant besides the modules themselves: combiner boxes, recombiners, inverters, junction boxes, connectors, cabling, trackers, and racking. The soft goods on this page, the gaskets, seals, insulators, wear pads, and protection, live at the interfaces of BOS hardware.
IEC 60529 IP code (by designation)
The two-digit ingress-protection code per IEC 60529 [3]: the first digit is solid/dust protection, the second is water. IP54 (dust-protected, splash), IP65 (dust-tight, low-pressure jets), IP66 (powerful jets); PV junction boxes commonly reach IP67/IP68 with potting. Held by the complete enclosure.
NEMA 250 Type 3R / 4 / 4X (by designation)
The enclosure Type designations per NEMA 250 [1]: Type 3R (rain, sleet, snow), Type 4 (hose-directed water, dust-tight), Type 4X (Type 4 plus corrosion resistance). The North American counterparts to the outdoor IP codes; earned by the complete tested enclosure.
IEC 62790 (by designation)
The standard for junction boxes for photovoltaic modules, safety requirements and tests to 1500 V DC, per [4] (dielectric, thermal-cycling, humidity-freeze, UV). It governs the J-box at the component level; the seals and dielectric barriers H-O converts sit inside that design.
IEC 62852 (by designation)
The standard for connectors for DC-application in photovoltaic systems (to 1500 V DC / 125 A), per [5b], with UL 6703 the US counterpart. The connector safety evaluation belongs to the tested connector; H-O supplies the seals and dielectric layers around it.
Compression set
The permanent deformation a gasket keeps after sustained compression; the property that decides whether a sealing force is still valid years later. Tested per ASTM D395 [8] for solids and ASTM D1056 methods for cellular grades. On a 25-year PV plant it is the controlling number over the service life.
Compression-deflection (CD)
The pressure a cellular material exerts at a given compression, the curve that turns a foam or sponge into a specifiable spring. Reported by class per ASTM D1056 [6]; match the gasket's CD class to the real closure force, not the gauge.
UV weathering & ozone resistance
The properties that keep an outdoor part from degrading under 25 years of sunlight and atmospheric ozone. Fluorescent-UV weathering is run per ASTM G154 [5] and ozone cracking per ASTM D1149 [7]. EPDM and silicone are the UV/ozone-stable chemistries; standard neoprene and SBR are not.
Durometer (Shore A)
The hardness of a solid elastomer, measured per ASTM D2240 [8b]. Feedthrough and J-box grommets are specified by durometer (typically ~30–80 Shore A) and interference; the right hardness seals without chafing or being too stiff to conform.
ePTFE vent membrane
Expanded PTFE in a microporous node-and-fibril film that passes air and water vapor but blocks liquid water, dust, and salt, per [14]. Die-cut as a breather disc, it equalizes enclosure pressure over the daily thermal cycle and stops internal condensation while preserving the IP / NEMA rating.
UHMW-PE / self-lubricating wear pad
Ultra-high-molecular-weight polyethylene, a self-lubricating polymer with a low coefficient of friction (PTFE class) and high abrasion resistance that runs dry with no re-greasing, per [13]. Die-cut as a tracker bearing wear pad or slip layer, it carries the maintenance-free rotational duty of a single-axis tracker for the plant life.
Thermal interface material (TIM)
An electrically insulating, thermally conductive pad that carries heat from a device to a heat sink while blocking electrical contact. Thermal impedance is measured per ASTM D5470 [12] at a stated pressure; in a PV inverter the pad sits between the power stages and the heat sink. Performance is pressure-dependent, so state the real mounting pressure.
Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
Standards, test methods & technical references
The standards, test methods, and maker technical data sheets cited throughout this page. Enclosure ratings and module / component standards are cited by designation: they are earned by the complete tested enclosure, module, or component, not by a gasket. Standards editions current as of July 2026; verify against the publishing body before final spec. H-O materials are aligned to the material-level standards through the source manufacturer's TDS, not independently certified by H-O unless explicitly stated on the quote.
[1] NEMA 250 (by designation)
NEMA 250 — Enclosures for Electrical Equipment (1000 Volts Maximum). Defines the enclosure Type designations, including outdoor Types 3R, 4, and 4X, evaluated on the complete enclosure. nema.org (NEMA 250)
[2] UL 50 / UL 50E (by designation)
UL 50 / UL 50E — Enclosures for Electrical Equipment, Environmental Considerations. The North American listing environment for the NEMA Type designations; cited by designation. shopulstandards.com (UL 50E)
[3] IEC 60529 (by designation)
IEC 60529 — Degrees of Protection Provided by Enclosures (IP Code). The two-digit dust/water ingress-protection code; the IEC counterpart to the NEMA Types, held by the complete enclosure. webstore.iec.ch (IEC 60529)
[4] IEC 62790 (by designation)
IEC 62790 — Junction boxes for photovoltaic modules: Safety requirements and tests (Ed. 2.0, 2020; to 1500 V DC). Covers the J-box dielectric, thermal-cycling, humidity-freeze, and UV testing at the component level; cited by designation. webstore.iec.ch (IEC 62790)
[5] ASTM G154
ASTM G154 — Standard Practice for Operating Fluorescent Ultraviolet (UV) Lamp Apparatus for Exposure of Nonmetallic Materials. The accelerated UV-weathering practice behind the 25-year outdoor durability of the EPDM and silicone parts on this page. astm.org (G154)
[5b] IEC 62852 (by designation)
IEC 62852 — Connectors for DC-application in photovoltaic systems: Safety requirements and tests (to 1500 V DC / 125 A), with UL 6703 the US counterpart. The connector safety evaluation belongs to the tested connector; cited by designation. webstore.iec.ch (IEC 62852)
[6] ASTM D1056
ASTM D1056 — Standard Specification for Flexible Cellular Materials, Sponge or Expanded Rubber. The classification and compression-deflection method behind the EPDM, silicone sponge, and polyethylene foam grades on this page. astm.org (D1056)
[7] ASTM D1149
ASTM D1149 — Standard Test Methods for Rubber Deterioration, Cracking in an Ozone Controlled Environment. The ozone-resistance method that separates outdoor-durable EPDM and silicone from commodity elastomers that craze. astm.org (D1149)
[8] ASTM D395
ASTM D395 — Standard Test Methods for Rubber Property, Compression Set. The method behind the compression-set values that decide whether a PV enclosure gasket keeps its sealing force over the 25-year service life. astm.org (D395)
[8b] ASTM D2240
ASTM D2240 — Standard Test Method for Rubber Property, Durometer Hardness. The Shore A hardness method for the solid-silicone grommets, J-box seals, and solid-sheet grades. astm.org (D2240)
[9] ASTM B117
ASTM B117 — Standard Practice for Operating Salt Spray (Fog) Apparatus. The salt-fog apparatus behind the corrosion exposure a NEMA 250 Type 4X enclosure adds over Type 4, and the coastal / marine PV exposure the gasket is chosen against. astm.org (B117)
[10] UL 94
UL 94 — Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances. The source of the V-0 flame class on the rated silicone-sponge grades; the class belongs to the material grade per its TDS. shopulstandards.com (UL 94)
[11] Rogers BISCO HT closed-cell TDS
Rogers Corporation BISCO HT closed-cell Medium Silicone Foam technical data sheet: a medium closed-cell silicone foam for outdoor enclosure sealing, service range roughly −67 to +392 °F (−55 to 200 °C), UL 94 V-0 flame rated, with low compression set. Values per the maker TDS. rogerscorp.com (BISCO HT closed-cell)
[12] ASTM D5470
ASTM D5470 — Standard Test Method for Thermal Transmission Properties of Thermally Conductive Electrical Insulation Materials. The thermal-impedance method behind the inverter TIM pad values; the impedance is measured at a stated pressure, so mounting pressure must be specified. astm.org (D5470)
[13] Polymer plain bearings for PV trackers
Industry technical reference for self-lubricating polymer plain bearings in single-axis PV tracking systems: UV-resistant, maintenance-free (no lubrication), low-friction bushings and wear surfaces sized for the tracker's 25-year rotational duty. UHMW-PE and PTFE wear surfaces run dry with a coefficient of friction in the PTFE class. igus.com (solar tracker bearings)
[14] Gore ePTFE Protective Vents
Gore ePTFE protective-vent technical reference: an expanded-PTFE microporous membrane that equalizes enclosure pressure and reduces condensation while blocking liquid water and dust, preserving the enclosure's IP / NEMA rating. gore.com (enclosure pressure relief)
Updated . Standards editions and links current at publication; verify against the publishing body before final spec. Enclosure ratings (IEC 60529, NEMA 250, UL 50E) and module / component standards (IEC 61215/61730, IEC 62790, IEC 62852) belong to the complete tested assembly; H-O materials are “aligned to” the material-level standards cited via the maker TDS. Lot-specific qualification documentation available on request.
To review your PV balance-of-system part, send:
- IEC 60529 IP or NEMA 250 Type target
- Hardware: enclosure, J-box, module, tracker, roof
- Door-channel, lid, or part geometry
- Latch / closure or bolt force
- Service temperature range (desert / rooftop)
- Flame-class and salt-exposure needs
- Cable / conduit / connector entry sizes
- Tracker bearing load and rotation duty
- Whether the enclosure is fully sealed (breather)
- Adhesive / liner requirements
- Prototype and annual volume
Get a PV balance-of-system materials quote
Send a drawing set, BOM, or hardware spec. We typically respond within one business day with a material-family recommendation, prototype lead time, and TDS verification against your rating target, temperature window, UV/ozone durability, flame and salt exposure, wear duty, and entry and breathing needs.
See also: related H-O application pages
Engineering content for the adjacent energy and power sub-applications and the parent hub. Each page covers material selection, failure modes, and converter-side process detail for its application family.
Sibling sub-application
Outdoor power & substation sealing
The deep outdoor-enclosure gasket playbook this page's combiner and inverter zones draw from: EPDM, silicone, cloth-inserted, butyl, and vent membranes.
Read the page
Sibling sub-application
Power systems thermal management
The full inverter TIM selection logic behind this page's thermal zone: gap fillers, insulating pads, and thermal impedance per ASTM D5470.
Read the page
Sibling sub-application
Power systems EMI shielding
The conductive-gasket and shielding playbook for inverter EMI control, the electromagnetic side of the same power-conversion enclosure.
Read the page
Sibling sub-application
Power equipment vibration & acoustic
Base isolation and acoustic materials for inverters, transformers, and rotating equipment in the energy environment.
Read the page
Industry hub
Energy, power & renewable
The full energy application family: insulation, thermal, EMI, sealing, arc-flash, vibration, and renewable infrastructure.
Read the page
Material data & standards. All compression, temperature, durometer, ozone, UV-weathering, salt-exposure, and thermal values on this page are taken from the source maker's technical data sheets with the method named (ASTM D1056, D2240, D1149, G154, D395, B117, D5470; UL 94 classes per the listed grade TDSs).
Enclosure ratings (IEC 60529 IP codes, NEMA 250 Type 3R/4/4X, UL 50/50E) and module / component standards (IEC 61215/61730, IEC 62790, IEC 62852) are cited by designation only: they are earned by the complete tested enclosure, module, or component, and the materials on this page support assemblies evaluated to them.
H-O converts gaskets, pads, insulators, and wear strips; H-O does not manufacture modules, cells, connectors, or inverters, does not certify or list enclosures, and does not independently certify materials against the standards unless explicitly stated on the quote. Verify against the maker TDS and your assembly-level evaluation plan.
Conversion scope. H-O and converts sheet, roll, and blanket stock to drawing in Winsted, Connecticut: die-cut and kiss-cut gaskets, grommets, and vent discs, slit films and tapes, waterjet-cut thick sections and wear pads, laminations, and kitted balance-of-system sets, with material traceability and lot-code TDS records. Molding and extrusion are not in-house processes; molded or extruded profiles are coordinated through a partner network. Lead-time and MOQ details are in the process strip and the quote form above.