Outdoor — IP-Rated & Harsh Environment Sealing
H-O Products die-cuts and converts EPDM, silicone solid and closed-cell BISCO® foam, fluorosilicone, FKM/Viton®, neoprene, PORON® microcellular urethane, and expanded-PTFE vent membrane into the perimeter gaskets, window seals, feedthrough seals, and pressure-equalization elements that carry the IP rating on outdoor IoT, telematics, kiosk, and camera enclosures, built to your drawing.
Built for: IP65 / IP66 / IP67 door and lid perimeter gaskets, display-window seals, cable-gland and connector feedthrough seals, ePTFE breather vents for pressure equalization and condensation control, and the UV, ozone, salt-fog, and fuel-splash resistance that outdoor sites demand, on sheet-metal and cast enclosures alike.
This guide is for the outdoor-electronics design and application engineers, and the procurement buyers who qualify their parts, specifying perimeter gaskets, window and feedthrough seals, and pressure-equalization vents for IoT, telematics, kiosk, camera, and roadside enclosures that have to hold an IP65 / IP66 / IP67 rating and survive UV, ozone, salt fog, thermal cycling, condensation, and fuel or chemical splash in the field.
To seal an outdoor IP-rated electronics enclosure, compress an elastomer or foam perimeter gasket between the lid and body to block the dust and fresh water that IEC 60529 measures, and add a hydrophobic expanded-PTFE vent membrane to equalize thermal-cycling pressure and control condensation.
For weather exposure, specify EPDM (the UV and ozone default) or silicone, with BISCO® closed-cell silicone foam where wide temperature range and low compression set matter. 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.
Enclosure-level, by designation (the rating belongs to the tested enclosure): IEC 60529 (IP code: dust and fresh water only) · NEMA 250 (U.S. enclosure Types; adds corrosion, icing, gasket aging, oil) · UL 50E (harmonized enclosure environmental Types, third-party inspected).
Material-level, per the maker TDS: ASTM B117 (salt spray/fog) · ASTM D1149 (ozone cracking) · ASTM G154 / G155 (fluorescent-UV and xenon-arc weathering) · ASTM D2240 (durometer) · ASTM D395 (compression set) · ASTM D1056 (flexible cellular rubber classes) · ASTM D471 (effect of liquids / fluid immersion) · UL 94 (flammability class on the rated grades).
- Weather perimeter gasket: EPDM or silicone
- Wide temp + low set: BISCO® closed-cell silicone foam
- Low-closure-force lid seal: silicone sponge
- Fuel / solvent splash: fluorosilicone or FKM/Viton®
- Economy / sheltered outdoor: neoprene foam
- Internal cushion / display pad: PORON® microcellular urethane
- Pressure equalization / condensation: ePTFE vent membrane
- Feedthrough / connector seal: solid silicone washers
Where are you in the spec process?
This page serves engineers who already know the gasket material they want and engineers still matching an elastomer to an outdoor environment and an IP target. 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 perimeter gasket, a fluorosilicone or FKM harsh-environment seal, a closed-cell foam window seal, an ePTFE breather vent, or a custom configuration on your drawing.
Skip to the quote form →Walk through outdoor-seal selection
Six selection factors (IP vs NEMA target, weather chemistry, temperature, enclosure mechanics, compression design, pressure equalization), an environment-vs-material selector, and seven material families with TDS-cited test methods.
Start with selection factors →
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1Send drawingUpload a DXF, STEP, or PDF, or describe the enclosure, the groove or land, and the IP target. A sample part works too.
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2Material reviewEngineering reviews the environment (UV, ozone, salt fog, temperature, fuel or chemical splash) and the enclosure mechanics against the vendor TDS, checks the compression the joint delivers, and frames the compliance language correctly: material classes (UL 94, ASTM D1056) by TDS, and IP / NEMA / UL Type ratings by designation, belonging to the tested enclosure.
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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, on flatbed die-cutting, CNC knife cutting for gasket outlines and vent-membrane parts, and slitting for strip seals. Ongoing parts run with material traceability and lot-code TDS records.
Ingress-protection requirement → environment and material selection → compression design → converted gasket + vent → production supply.
- 1IP / NEMA requirementFix the IP target (IP65/66/67) and whether a NEMA/UL Type is contractually required.
- 2Read the environmentUV/ozone, temperature range, salt fog, condensation, and any fuel or chemical splash.
- 3Choose material familyEPDM or silicone for weather; fluorosilicone or FKM for harsh chemistry; ePTFE for venting.
- 4Design the compressionMatch gasket construction and target compression to the enclosure's closure force and joint.
- 5Die-cut to drawingPerimeter gasket, window seal, feedthrough washer, or vent element cut with sealed edges.
- 6Quote prototype or productionPrototype quantities through full production runs, with the TDS and lot-code records.
What are you sealing?
Application Zones
Sealing an outdoor enclosure is really several problems that share a wall: the continuous perimeter gasket that carries the IP rating on the door or lid; the window and display seal that keeps the same rating across a viewing aperture; the connector and cable-gland feedthroughs, where every penetration is a leak candidate; the breather vent that equalizes the pressure a sealed box builds as it heats and cools; the difference between sealing a stiff cast enclosure and a flexing sheet-metal cover; and the harsh-chemistry edge where fuel, solvent, or salt defeats the weather elastomers.
Click a tab to see the joint, the controlling properties, and the families H-O converts for that zone.
Door & lid perimeter gaskets: the seal that carries the IP rating
The continuous gasket between the cover and the enclosure body is what an IP test actually measures: compress it enough to close the dust and water paths, keep it compressed as the box thermally cycles for years, and shrug off the UV and ozone that embrittle the wrong rubber.
EPDM is the outdoor default because its backbone resists UV, ozone, and weathering (the reason it displaced neoprene for weather sealing), with a service range roughly -50 to +150 °C on the TDS; silicone solid and closed-cell BISCO® foam extend the temperature range to about -55 to +200 °C with excellent UV, ozone, and low compression-set behavior.
Neoprene serves sheltered, economy duty. The gasket is specified by durometer (ASTM D2240), compression set (ASTM D395), and, for cellular grades, an ASTM D1056 class, and the IP / NEMA rating that results belongs to the assembled enclosure, not to the part. [1]
Window, display & feedthrough seals: the aperture and penetration problem
Every aperture and every penetration in an outdoor enclosure is a place the perimeter seal can be undone. A display or camera window needs a frame gasket that bonds the polycarbonate or glass to the bezel and holds the same IP rating across the viewing opening; a connector or cable-gland feedthrough needs flat washers, port plugs, and grommet-style seals so the wall stays sealed where cables enter.
Silicone solid is the natural choice for window and feedthrough seals: wide temperature range, excellent UV and ozone life, and clean die-cutting into thin frames and washers; EPDM covers the same forms where fuel is absent and cost leads. The controlling idea is systemic, not per-part: the enclosure only earns its rating when the gaskets at the perimeter, the window, and every feedthrough are specified together, so H-O the full set to one drawing package with sealed, accurate edges.
Venting & pressure equalization: the seal's quiet partner
A perfectly sealed outdoor box has a second problem hiding inside it. As the enclosure heats in the sun and cools at night it breathes, and the pressure differential either stresses the perimeter seal or draws humid air past it, where the moisture condenses on cold electronics.
The answer is a hydrophobic, oleophobic expanded-PTFE vent membrane: it lets air and water vapor pass to equalize pressure, but blocks liquid water, dust, salt, and oil, so the perimeter gasket is never fighting a pressure gradient and condensation is controlled by bidirectional air exchange.
Screw-in ePTFE vents carry high IP ratings and mechanical-impact ratings in their own housings; ePTFE membrane discs and adhesive-mounted vents cover the same job where the enclosure integrates its own port. H-O the membrane discs and the sealing gaskets around them to the vent-port drawing.
Cast vs sheet-metal enclosures: closure force sets the gasket
The same IP target is a different gasket problem on a cast enclosure than on a sheet-metal one, and mixing them up is a common leak. A rigid cast enclosure with a machined groove can deliver high, even closure force, so it takes a firmer solid gasket compressed into a controlled band. A thin sheet-metal cover flexes between its fasteners, so closure force is uneven and low: it needs a soft, low-closure-force sponge or foam gasket that conforms across the span, or the seal is only good at the bolts and leaks mid-span.
Compression is the number that ties it together: solid gaskets are typically designed to roughly 15–25% compression and hollow or sponge profiles to about 25–40%, with groove depth set so the gasket is neither starved of squeeze nor over-compressed into an early set. State the enclosure construction, the closure method, and the groove or land geometry, and the gasket construction and compression target follow.
Harsh chemical, fuel splash & salt fog: past the weather elastomers
At fueling stations, roadside cabinets, and industrial sites the environment reaches past what EPDM and general silicone were compounded for.
Fuel and non-polar solvents call for fluorosilicone (FVMQ), which adds trifluoropropyl chemistry for resistance to fuels, oils, and solvents while keeping silicone-like low-temperature flexibility and low compression set, with a service range near -60 to +200 °C on the TDS; the most aggressive chemistry or the hottest fuel duty steps up to FKM/Viton®, which resists fuels and aggressive chemicals more broadly than any other elastomer on this page though it is weaker in the cold than fluorosilicone.
Coastal and roadside salt fog is a corrosion problem the IP code does not cover: it is where the NEMA 4X / UL Type 4X framing and salt-spray testing per ASTM B117 belong. Name the fluid, its concentration, and the temperature on the drawing; compatibility is read from the maker TDS and ASTM D471 immersion data, never assumed from the family name.
Six decisions that drive your outdoor-seal spec
An outdoor enclosure seal satisfies several independent constraints at once, and missing one produces a joint that passes the bench IP test, ships fine, and lets water in a year later after the elastomer has embrittled in UV, taken a compression set, or been asked to hold back a fluid it was never compounded for.
An IP rating belongs to the enclosure, not to the gasket, and it covers only dust and fresh water. IEC 60529 says nothing about corrosion, icing, or gasket aging: those live in a NEMA 250 / UL 50E Type rating. Write the material's own classes (durometer, ASTM D1056 class, UL 94) on the part callout, cite IP / NEMA / UL by designation, and never let a drawing imply a gasket is "IP67 rated": the gasket supports an enclosure evaluated to it.
The IP two-digit code measures exactly two things: solid-particle (dust) ingress in the first digit (0–6) and water ingress in the second (0–8, plus 9/9K). IP65 is dust-tight plus water jets, IP66 dust-tight plus powerful jets, IP67 dust-tight plus 30-minute immersion to 1 m. Water ratings are not cumulative above IPX6, so a device needing both jet and immersion protection is dual-rated. The gasket on this page is the ingredient of that result; the rating belongs to the tested enclosure.
Read the six factors below in order. The first sets the target (IP vs NEMA), the next two read the environment (weather chemistry, temperature), the fourth and fifth build the seal (enclosure mechanics, compression), and the last closes the pressure loop (venting). Every factor names its test method, because in outdoor service the documentation is part of the part.
Show all 6 selection factors tap to expand
Target first: IP is dust and water, NEMA/UL adds the rest
Rule — fix the IP number and decide whether a NEMA/UL Type is contractually required before choosing a material. IEC 60529 rates dust (first digit) and fresh water (second digit) only; NEMA 250 and the harmonized UL 50E add corrosion resistance, effects of icing, gasket aging, and oil resistance, and only a listed enclosure can claim them [3]. The mapping is one-way: a NEMA 4X enclosure can be said to meet IP66, but an IP66 box is never a NEMA 4X because it was never corrosion- or ice-tested.
Write the IP target and any NEMA/UL Type on the drawing; the material and the qualification test set fall out of it. [2]
Weather chemistry: UV and ozone pick the elastomer family
Rule — outdoors, the elastomer is chosen by what sunlight and air do to it before anything else. Ozone attacks strained rubber surfaces (the mechanism ASTM D1149 measures) and UV embrittles and chalks, so EPDM and silicone (both excellent in UV and ozone) own the weather perimeter, and neoprene (ozone-limited) stays in sheltered, economy duty. Fuel or aggressive solvent overrides this: those need fluorosilicone or FKM regardless of the weather answer.
State the outdoor exposure and any fuel or chemical splash on the drawing, and hold the family boundary: a great mechanical gasket in the wrong chemistry cracks first. [5]
Temperature range: the cold end disqualifies as often as the hot
Rule — outdoor enclosures see wide daily and seasonal swings, and the low-temperature limit disqualifies materials as readily as the high. EPDM covers roughly -50 to +150 °C; silicone and BISCO® closed-cell foam stretch to about -55 to +200 °C; fluorosilicone keeps silicone-like cold flexibility to about -60 °C while adding fuel resistance; FKM is chemically strong but stiffens in the cold unless a low-temperature grade is specified.
State the continuous and the extreme temperatures at the gasket, not the room ambient, and confirm the family's TDS range covers both ends with margin. [11]
Enclosure mechanics: cast takes a solid, sheet-metal takes a sponge
Rule — the enclosure's stiffness and closure force pick the construction. A rigid cast enclosure with a machined groove delivers high, even closure force and takes a firmer solid gasket; a thin sheet-metal cover flexes between fasteners, so closure force is low and uneven and it needs a soft, low-closure-force sponge or foam that conforms across the span, or the seal is only good at the bolts.
Tell H-O whether the enclosure is cast or sheet-metal, the closure method, and the groove or land geometry; a gasket that needs more seating force than the joint can deliver leaks regardless of material. [14]
Compression design: enough squeeze to seal, not enough to set
Rule — the seal lives or dies on how far the gasket is compressed. Under-compress and the ingress path never closes; over-compress and the gasket takes a permanent set that opens a gap once the fasteners relax. Solid gaskets are typically designed to roughly 15–25% compression and hollow or sponge profiles to about 25–40%, with groove depth set to hold that band, and compression-set resistance (ASTM D395; the ASTM D1056 class for cellular grades) is what keeps the band alive over years of thermal cycling.
Put the target compression and the compressed thickness on the drawing; those two numbers plus the closure force pick the durometer and gauge. [8]
Pressure equalization: seal the box, then let it breathe
Rule — a sealed outdoor box builds a pressure differential as it heats and cools, and that differential either stresses the perimeter seal or draws humid air past it to condense inside.
A hydrophobic, oleophobic expanded-PTFE vent membrane equalizes the pressure and controls condensation by bidirectional air exchange while blocking liquid water, dust, salt, and oil, so the gasket never fights a gradient. Give H-O the enclosure's internal volume and the expected thermal swing so the vent membrane and its port gasket are sized to the breathing the box will actually do. [12]
Specification Tools
Two tools to take you from "my enclosure lives outdoors" to here's the material and sealing approach for the drawing: an environment-driven outdoor-seal selector that maps your exposures to the gasket family and flags whether a breather vent is warranted, and a side-by-side comparison of every outdoor-sealing family on this page.
1. Outdoor seal selector (environment → material approach)
Pick the dominant outdoor exposure and the enclosure construction. The selector returns a recommended material family, a starting compression band, and whether a pressure-equalization vent is warranted, plus the citation language (material classes per TDS; IP / NEMA ratings by designation, belonging to the tested enclosure). It is a starting point for the drawing note, not a substitute for the TDS or an IP test.
Recommended: EPDM or silicone perimeter gasket
EPDM is the outdoor UV and ozone default for weather exposure; silicone extends the temperature range. On a cast enclosure with a machined groove, a firmer solid gasket compressed to roughly 15–25% suits the even, high closure force.
1b. The same logic, printed: exposure × material quick reference
The full map behind the selector, readable without touching a control. PF = preferred fit · C = conditional, verify the grade's TDS · GA = generally avoided.
| Family | Sun / UV / ozone | Wide temp swing | Salt fog / coastal | Fuel / solvent splash | Aggressive chemical | Low-closure-force lid |
|---|---|---|---|---|---|---|
| EPDM (solid & foam) | PF | C | PF | GA | C (aqueous) | C (foam grade) |
| Silicone (solid + BISCO® foam) | PF | PF | PF | GA | C | PF (sponge/foam) |
| Fluorosilicone (FVMQ) | PF | PF | PF | PF | C (verify grade) | PF (sponge) |
| FKM / Viton® | PF | C (cold-limited) | PF | PF | PF (most) | C (sponge) |
| Neoprene (CR) | GA (ozone-limited) | C | C | C (oils) | GA | PF (foam) |
| PORON® microcellular urethane | C (internal) | C | GA (wet path) | GA | GA | PF (cushion pad) |
| Expanded-PTFE vent membrane | PF (venting) | PF | PF | PF (oleophobic) | PF (inert) | n/a (vent, not gasket) |
2. Side-by-side: outdoor-sealing family comparison matrix
Every outdoor-sealing family called out on this page, with construction, the property class that drives its selection, the standards its TDS cites, and the duty it fits. Click a column header to sort. Click any material name to jump to its accordion entry and full TDS reference.
| Material | Construction | Selection class | Standards on the TDS | Best for | |
|---|---|---|---|---|---|
| Weather perimeter (UV / ozone / temperature) | |||||
| EPDM (Solid & Foam)Ethylene-propylene-diene | Solid + closed-cell foam | UV / ozone weather life | ASTM D2240, D395, D1149; ~ -50 to +150 C | Weather perimeter default | |
| Silicone (Solid + BISCO® Foam / Sponge)VMQ, incl. closed-cell foam | Solid + sponge/foam | Wide temp + low set | ASTM D1056, D395; UL 94 (foam); ~ -55 to +200 C | Wide-temp perimeter, windows | |
| Neoprene (CR) Foam & SolidPolychloroprene | Closed-cell foam / solid | Economy (ozone-limited) | ASTM D1056; ~ -40 to +100 C | Sheltered / economy outdoor | |
| Harsh chemistry & fuel | |||||
| Fluorosilicone (FVMQ) SpongeTrifluoropropyl silicone | Closed-cell sponge | Fuel + cold flexibility | ASTM D471, D1056; ~ -60 to +200 C | Fuel / solvent splash seals | |
| FKM / Viton® (Solid + Sponge)Fluoroelastomer | Solid + closed-cell sponge | Aggressive chemistry | ASTM D471, D2240 (per TDS) | Most aggressive fuels / chemicals | |
| Cushion & venting | |||||
| PORON® Microcellular UrethaneMicrocellular PU | Microcellular PU foam | Compression-set resistance | ASTM D3574 (per TDS); ~ -40 to +90 C | Internal cushion / display pads | |
| Expanded-PTFE Vent MembraneHydrophobic ePTFE | Microporous ePTFE | Airflow vs water-entry | Maker TDS (IP / airflow / impact) | Pressure equalization / condensation | |
Skip ahead and request your engineering review now
If your drawing already calls out an EPDM or silicone perimeter gasket, a fluorosilicone or FKM harsh-environment seal, a foam window seal, or an ePTFE breather vent, send it over for engineering review against the environment and the enclosure.
Outdoor-seal failures you can prevent at spec
Outdoor-seal failures rarely show at the factory. The gasket seats, the IP test passes, the unit ships. Then water gets in months or years later, after UV embrittled the rubber, a compression set opened a gap, condensation built up with nowhere to vent, or a fuel splash swelled a gasket that was never meant for it. Five patterns cover most of what fails on outdoor enclosures, and each one is a specification decision made before the first part is cut.
The IP test on day one does not predict year three. UV embrittlement, compression set, and condensation play out slowly and do not reverse. The fix is at spec, against the material's UV, ozone, and compression-set data (ASTM D1149, G154/G155, D395) and a breather-vent decision, not at the field-return bench.
Show all 5 failure modes tap to expand
1. The gasket embrittled in the sun and cracked at a strain
A perimeter gasket chosen for its mechanical fit outdoors, in a rubber with poor weathering, chalks and hardens in UV and then cracks where the groove holds it in strain, exactly the ozone-attack mechanism ASTM D1149 measures.
Neoprene and other non-weather rubbers are the usual culprits; the joint that sealed fine indoors weeps after a season of sun. Fix — hold the family boundary: use EPDM or silicone for weather perimeters (both excellent in UV and ozone), reserve neoprene for sheltered economy duty, and specify the ozone and accelerated-weathering data (ASTM D1149, G154/G155) on the material callout so the review happens against numbers, not adjectives.
2. The seal took a compression set and quietly opened a gap
A gasket specified by thickness rather than compression, or over-compressed into a shallow groove, takes a permanent set under sustained load and heat: it no longer rebounds, and once the fasteners relax with thermal cycling a gap opens and the IP seal is lost.
The failure is invisible until it rains hard enough. Fix — design the compression, not the thickness: put a target compression (roughly 15–25% solid, 25–40% sponge) and a compressed thickness on the drawing, size the groove depth to hold that band, and pick a grade whose compression-set data (ASTM D395; the ASTM D1056 class for cellular grades) keeps the band alive over years.
3. The box was sealed too well, and condensation formed inside
A fully sealed outdoor enclosure breathes as it heats and cools, and with nowhere to equalize, the pressure differential either stresses the perimeter seal or draws humid air past it, where it condenses on cold electronics.
The paradox is that a better seal made the condensation worse. Fix — pair the seal with a hydrophobic, oleophobic expanded-PTFE breather vent sized to the enclosure's internal volume and thermal swing: it equalizes pressure and controls condensation by bidirectional air exchange while blocking water, dust, salt, and oil, so the gasket never fights a gradient.
Give H-O the internal volume and the temperature range with the drawing. [12]
4. The sheet-metal cover sealed at the bolts and leaked between them
A firm solid gasket picked for a rigid enclosure is dropped onto a thin sheet-metal cover that flexes between its fasteners: closure force is high at the bolts and low mid-span, so the seal is only good where the fasteners pull, and water finds the gap in between. The same happens in reverse when a groove is machined too shallow for the gasket.
Fix — match the construction to the enclosure: a low-closure-force silicone or fluorosilicone sponge or closed-cell foam that conforms across the span for flexing sheet-metal covers, a firmer solid in a controlled compression band for stiff cast enclosures. Tell H-O the enclosure construction and closure method with the drawing. [14]
5. A fuel or salt exposure defeated a weather-only gasket
An EPDM or general-silicone perimeter gasket, correct for sun and rain, goes onto an enclosure at a fueling station or a coastal roadside cabinet, and the fuel splash swells it or the salt-fog corrosion problem it was never rated for goes unaddressed.
The gasket "was rated for outdoors," but outdoors meant weather, not fuel or salt. Fix — name the specific exposure: step to fluorosilicone for fuel and solvent splash or FKM/Viton® for the most aggressive chemistry (verify the grade against ASTM D471 immersion data), and treat coastal salt fog as the corrosion problem it is, with the NEMA 4X / UL Type 4X framing and ASTM B117 salt-spray testing at the enclosure level.
Material reference
Detailed specs for the seven outdoor-sealing families referenced on this page: the weather perimeter set (EPDM, silicone solid and closed-cell BISCO® foam, and economy neoprene); the harsh-environment set (fluorosilicone for fuel and solvent, FKM/Viton® for aggressive chemistry); the internal cushion (PORON® microcellular urethane); and the pressure-equalization element (expanded-PTFE vent membrane).
Values are taken from the maker TDS on file for each grade, with the test method named; IP / NEMA / UL Type ratings are cited by designation only, belonging to the tested enclosure.
H-O die-cuts, kiss-cuts, slits, and laminates every family to drawing in low and high volume.
EPDM Solid & Foam (Outdoor Weather Default)UV / ozone / weather perimeter gaskets · ~ -50 to +150 °C · ozone per ASTM D1149
Specify solid vs foam by the enclosure mechanics (solid for cast grooves, foam for flexing sheet-metal covers), the durometer, and the temperature range. The IP / NEMA rating that results belongs to the assembled enclosure; the EPDM grade carries its own ASTM classes on the TDS.
Silicone Solid + BISCO® Closed-Cell Foam & SpongeWide temperature range, low compression set · ~ -55 to +200 °C · UL 94 class on the foam TDS
Specify form first (solid vs foam vs sponge), then the temperature range and any flame class. The BISCO® foam grades carry their own UL 94 listing per the individual grade TDS; the material class is the gasket's, and the enclosure's IP / NEMA rating is the enclosure's.
Neoprene (CR) Foam & Solid (Economy / Sheltered)Economy weather gaskets · ~ -40 to +100 °C · better oil resistance than EPDM, ozone-limited
Specify neoprene where cost leads and the exposure is sheltered; move to EPDM or silicone the moment prolonged UV and ozone are in play. Rebonded neoprene serves the load-bearing pad duty rather than the perimeter seal.
Fluorosilicone (FVMQ) Sponge (Fuel & Chemical Resistant)Fuel / solvent splash seals with silicone cold flexibility · ~ -60 to +200 °C
Specify fluorosilicone by naming the fuel or solvent and the temperature; compatibility is read from the maker TDS and ASTM D471 immersion data, never assumed. Where chemical aggressiveness outranks cold flexibility, step to FKM.
FKM / Viton® (Solid + Sponge, Aggressive Chemistry)The broadest fuel & chemical resistance here · the step past fluorosilicone where chemistry leads
Specify form first (solid vs sponge), then verify the specific grade against the maker's chemical-compatibility table and ASTM D471 immersion data at your concentration and temperature. FKM is the deliberate step-up when chemistry outranks cold flexibility.
PORON® Microcellular Urethane (Internal Cushion)Display back-pads & low-load cushion gaskets · ~ -40 to +90 °C · compression-set resistance
Specify PORON® for internal cushioning and low-load compression duty; keep it out of the perimeter and feedthrough wet path, where a closed-cell weather elastomer belongs. The EV and battery compression-pad playbook applies directly to its internal role.
Expanded-PTFE Vent Membrane (Pressure Equalization)Hydrophobic / oleophobic breather membrane · passes air, blocks water, dust, salt & oil
Size the vent to the enclosure's internal volume and thermal swing so it equalizes fast enough without over-venting; the membrane's airflow-vs-water-entry pairing is per the maker TDS. The added port is itself a penetration, so seal around it with a silicone or fluorosilicone port gasket.
6113-05 Virgin, Skived PTFEPublished product data · verify grade against the TDS
PTFE Film & Coated FiberglassPTFE-Coated Fiberglass (vent support)
Solid Silicone RubberSolid Silicone / EPDM (cast, machined groove)
Silicone Sponge — BISCO® 7xxx SeriesSilicone Sponge (span-conforming)
Outdoor & IP-rated sealing: engineer-grade FAQ
Twelve of the questions we hear most from outdoor IoT, telematics, kiosk, and camera teams. If your question isn't here, send a drawing or call, engineering picks up.
What is the difference between IP65, IP66, and IP67?
All three are dust-tight (the first IP digit is 6). They differ in the water test: IP65 withstands water jets from a 6.3 mm nozzle, IP66 withstands powerful water jets from a 12.5 mm nozzle, and IP67 withstands 30-minute immersion to 1 m. Because the water ratings are not cumulative above IPX6, an IP67 rating does not by itself guarantee IPX5/IPX6 jet resistance, so a device that must survive both jets and immersion is dual-rated (for example IP66/IP68). All three are defined by IEC 60529 and cover dust and fresh water only. [1]
Is an IP rating the same as a NEMA rating?
No. An IEC 60529 IP code measures only dust and fresh-water ingress. A NEMA 250 Type rating (and the harmonized UL 50E) adds requirements the IP code never checks: corrosion resistance, the effects of icing, gasket aging, and oil resistance, and a listed enclosure is third-party inspected. The mapping is one-way: a NEMA 4X enclosure can be said to meet IP66, but an IP66 box is never a NEMA 4X because it was never corrosion- or ice-tested.
If your program requires corrosion or icing performance, specify the NEMA/UL Type, not just the IP number. [2]
If my enclosure is IP67, does that also mean IP65?
Not necessarily. The dust digit is cumulative (IP6X covers all lower dust levels), but the water digit is not above IPX6. IPX7 (immersion) is a different test from IPX5/IPX6 (jets), and passing immersion does not prove jet resistance. If your device sees both pressure-washing and temporary submersion, it needs a dual rating such as IP66/IP68. State both water conditions on the requirement so the enclosure and its gaskets are tested for both. [1]
EPDM or silicone for an outdoor gasket: which resists UV and ozone better?
Both are excellent outdoors, and the choice usually comes down to temperature and closure force. EPDM is the economical weather default with a service range around -50 to +150 °C and strong UV, ozone, and weathering resistance (ozone tested per ASTM D1149).
Silicone stretches the temperature range to about -55 to +200 °C with equally good UV/ozone life and lower compression set, and its closed-cell foam and sponge forms seat at the low closure forces thin covers deliver. Pick EPDM for cost-led weather perimeters, silicone for wide temperature range, low-closure-force lids, and windows. [5]
When do I need fluorosilicone or FKM instead of EPDM or silicone?
When fuel, oil, or aggressive solvent touches the seal. EPDM and general silicone are weather elastomers and swell in hydrocarbons. Fluorosilicone (FVMQ) adds fuel and solvent resistance while keeping silicone-like cold flexibility (roughly -60 to +200 °C), which suits outdoor fueling and roadside sites.
FKM/Viton® is the step past that for the most aggressive chemistry, at the cost of weaker cold flexibility unless a low-temperature grade is specified. Name the fluid and its concentration; the grade is verified against the maker TDS and ASTM D471 immersion data. [6]
How much should I compress an outdoor enclosure gasket?
As a starting point, solid gaskets are commonly designed to roughly 15–25% compression and hollow or sponge profiles to about 25–40%, with groove depth set so the gasket holds that band. Too little compression and the ingress path never closes; too much and the gasket takes a permanent compression set that later opens a gap.
These bands are engineering and vendor guidance, not a mandated standard, so the final number comes from the grade's compression-set behavior (ASTM D395; the ASTM D1056 class for cellular grades) and the closure force the enclosure actually delivers.
Put the target compression and compressed thickness on the drawing. [14]
Why does my sealed outdoor enclosure get condensation inside, and how does a vent fix it?
A sealed box breathes: as it heats in the sun and cools at night, the internal pressure rises and falls, and with nowhere to equalize, that gradient either stresses the perimeter seal or draws humid air past it, where the moisture condenses on cold electronics. A hydrophobic, oleophobic expanded-PTFE breather vent equalizes the pressure and controls condensation by bidirectional air exchange, while blocking liquid water, dust, salt, and oil, so the gasket never fights a gradient. Size the vent to the enclosure's internal volume and thermal swing. [12]
What IP rating can an ePTFE breather vent reach?
Housed screw-in ePTFE vents are rated high: the membrane is hydrophobic and oleophobic, and the vent housings carry IP ratings up to IP68 (and, on all but the most compact, IP69K), along with mechanical-impact ratings (up to IK10) and a UL 94 V-0 flame class per the maker data. The vent adds a controlled breathing path without lowering the enclosure's ingress protection, which is the whole point. The membrane's airflow-vs-water-entry pairing determines how fast it equalizes; H-O membrane discs and their port gaskets to your vent-port drawing. [12]
How is a gasket for a cast enclosure different from one for sheet metal?
By closure force. A rigid cast enclosure with a machined groove delivers high, even closure force, so it takes a firmer solid gasket compressed into a controlled band. A thin sheet-metal cover flexes between fasteners, so closure force is low and uneven and it needs a soft, low-closure-force sponge or closed-cell foam that conforms across the span, or the seal is good only at the bolts and leaks mid-span. Tell H-O whether the enclosure is cast or sheet-metal, the closure method, and the groove or land geometry, and the construction follows. [14]
What does a salt-fog (ASTM B117) or ozone (ASTM D1149) test tell me?
They cover the two harsh-environment aging paths the IP code ignores. ASTM B117 runs a continuous 5% salt fog at about 35 °C to reveal corrosion of fasteners and sealing surfaces, the coastal and roadside failure mode behind NEMA 4X. ASTM D1149 exposes strained rubber to controlled ozone and rates the cracking, which is why ozone-limited elastomers like neoprene are kept out of prolonged-sun perimeters and EPDM and silicone are preferred. Accelerated UV weathering adds ASTM G154 (fluorescent UV) or G155 (xenon-arc). [4]
Can an IP66 enclosure be called NEMA 4X?
Not automatically. NEMA 4X requires corrosion resistance and icing performance that IP66 never tests, so an IP66 enclosure cannot claim NEMA 4X on the strength of its IP rating alone. The reverse is fine: a NEMA 4X enclosure can be stated to meet IP66, because it was tested to the more demanding set. If your drawing needs NEMA 4X, specify it explicitly and expect the corrosion and icing evaluation; the perimeter gasket (typically EPDM or silicone) supports that design but does not confer the rating. [2]
What should I send H-O so the outdoor-sealing quote comes back right the first time?
Seven things: (1) the IP target and any NEMA/UL Type requirement; (2) the enclosure construction, cast or sheet-metal; (3) the groove or land geometry and the closure force or method; (4) the outdoor exposures, UV/ozone, salt fog, and any fuel or chemical splash; (5) the operating and extreme temperature range; (6) whether a breather vent is needed, with the enclosure's internal volume and thermal swing; and (7) quantity for prototype and production, plus any adhesive or liner needs.
"Recommend the material" is a valid callout: that is what the engineering review is for. Material classes are cited per TDS; the IP / NEMA rating belongs to the tested enclosure.
Glossary: terms used on this page
Quick reference for the ingress-protection, weathering, and sealing terminology used throughout. Each entry links to the relevant standard or test method where applicable.
IP code (IEC 60529)
The two-digit Ingress Protection code per IEC 60529 [1]: the first digit (0–6) rates solid-particle and dust protection, the second (0–8, plus 9/9K) rates water. It covers dust and fresh water only, and the rating belongs to the assembled enclosure, not to a gasket.
NEMA 250 / UL 50E Type
The U.S. enclosure Type ratings per NEMA 250 [2] and the harmonized UL 50E: outdoor Types 3R/3S/4/4X/6/6P add corrosion, icing, gasket-aging, and oil requirements the IP code omits. The mapping to IP is one-way (a NEMA 4X can be said to meet IP66, but not the reverse).
Ingress path
Any route by which dust or water can enter an enclosure: the door or lid perimeter, a display window, a connector or cable-gland feedthrough, or an unsealed vent port. The IP rating holds only when every path is sealed as one system, so a single unsealed feedthrough can undo a good perimeter gasket.
Pressure equalization
Letting a sealed enclosure equalize the internal-vs-external pressure differential it builds as temperature changes, using a hydrophobic ePTFE vent membrane [12] that passes air but blocks liquid water, dust, salt, and oil. It removes the load on the perimeter seal and controls condensation without opening an ingress path.
Expanded PTFE (ePTFE) membrane
PTFE expanded into a microporous, hydrophobic and oleophobic film used as a breather vent: it passes air and water vapor for pressure equalization while blocking liquid water, dust, salt, and oil. The airflow-vs-water-entry pairing on the maker TDS sets how fast a given membrane equalizes.
UV & ozone resistance
The ability of a rubber to resist sunlight embrittlement and ozone cracking outdoors. Ozone attacks strained rubber surfaces, the mechanism measured per ASTM D1149 [5]; accelerated UV weathering uses ASTM G154/G155. EPDM and silicone excel here; neoprene is ozone-limited.
Compression set
The permanent deformation an elastomer keeps after long compression, per ASTM D395 [8] (reported as a percentage). High set means lost recovery, and lost recovery means a gasket that stops sealing as fasteners relax and the box thermally cycles: one of the main outdoor-seal failure paths.
Salt fog (ASTM B117)
A continuous salt-spray corrosion test (about 5% NaCl at 35 °C) per ASTM B117 [4]. It reveals corrosion of fasteners and sealing surfaces on coastal and roadside enclosures, the failure the IP code does not cover and the NEMA 4X Type rating does.
Durometer (ASTM D2240)
The hardness of a rubber, most often on the Shore A scale, per ASTM D2240 [7]. Durometer sets how much closure force a gasket needs to seal: a softer grade conforms to a flexing cover at low force, a firmer grade suits a stiff cast groove at higher force.
Cellular rubber class (ASTM D1056)
The classification for sponge and expanded rubber per ASTM D1056 [9]: Type 1 open-cell or Type 2 closed-cell, with classes and a compression-deflection grade. Closed-cell (Type 2) foams are the ones that seal outdoors, because open cells wick water.
Fluorosilicone (FVMQ)
Silicone with trifluoropropyl groups added for fuel, oil, and solvent resistance [10] while keeping silicone-like low-temperature flexibility and low compression set (roughly -60 to +200 °C). The outdoor answer where fuel or solvent splash defeats EPDM and general silicone.
FKM / fluoroelastomer
The fluorinated elastomer family (Viton® is a well-known trade name) with the broadest resistance to aggressive fuels and chemicals of the elastomers here, verified per ASTM D471 [6] immersion. Its trade-off outdoors is weaker cold flexibility than fluorosilicone unless a low-temperature grade is specified.
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-level ratings (IP, NEMA, UL Type) are cited by designation: they evaluate the assembled enclosure, and the rating belongs to the tested unit. Standards editions current as of July 2026; verify against the publishing body before final spec. H-O converts materials tested to the material-level methods on the source maker's TDS; H-O does not certify enclosures or independently certify materials unless explicitly stated on the quote.
[1] IEC 60529 (IP Code)
Degrees of Protection Provided by Enclosures (IP Code). Consolidated edition 2.2 (1989 + A1:1999 + A2:2013). Defines the two-digit dust and water ingress classes; covers fresh water only. Cited by designation; the rating belongs to the tested enclosure. iec.ch (IP ratings)
[2] NEMA 250 (by designation)
Enclosures for Electrical Equipment (1000 Volts Maximum). Defines the U.S. Type ratings (3R/3S/4/4X/6/6P for outdoor) that add corrosion, icing, gasket-aging, and oil requirements beyond the IP code. Cited by designation. nema.org (standards)
[3] UL 50E (by designation)
Enclosures for Electrical Equipment, Environmental Considerations. Harmonized with NEMA 250; the UL Type ratings match the NEMA Types and add third-party inspection. Cited by designation. shopulstandards.com (UL 50E)
[4] ASTM B117
Standard Practice for Operating Salt Spray (Fog) Apparatus. The continuous 5% NaCl fog test at about 35 °C behind coastal and roadside corrosion evaluation and the NEMA 4X duty on this page. astm.org/b0117
[5] ASTM D1149
Standard Test Methods for Rubber Deterioration – Cracking in an Ozone Controlled Environment. Cited on the EPDM and silicone TDSs; the reason those families own the outdoor perimeter while neoprene stays in sheltered duty. astm.org/d1149
[6] ASTM D471
Standard Test Method for Rubber Property – Effect of Liquids. The fluid-immersion method behind the fuel and chemical compatibility of the fluorosilicone and FKM grades on this page. astm.org/d0471
[7] ASTM D2240
Standard Test Method for Rubber Property – Durometer Hardness. The Shore A hardness method that sets the closure force a gasket needs; cited across the elastomer TDSs on this page. astm.org/d2240
[8] ASTM D395
Standard Test Methods for Rubber Property – Compression Set. The compression-set method behind the "enough squeeze to seal, not enough to set" factor; low compression set is what keeps an outdoor gasket sealing through years of thermal cycling. astm.org/d0395
[9] ASTM D1056
Standard Specification for Flexible Cellular Materials – Sponge or Expanded Rubber. The class (Type 2 closed-cell) and compression-deflection grade behind the foam and sponge gaskets on this page. astm.org/d1056
[10] Fluorosilicone (FVMQ) TDS — Stockwell Elastomerics
Maker technical data for fluorosilicone (FVMQ) solid and sponge: fuel, oil, and solvent resistance with silicone-like low-temperature flexibility, service range about -60 to +200 °C. The source for the fuel-splash zone on this page. stockwell.com (fluorosilicone)
[11] BISCO® HT silicone foam TDS — Rogers Corporation
Maker technical data for BISCO® HT-series closed-cell silicone foam: service range about -55 to +200 °C, low compression set, UV/ozone resistance, and UL 94 V-0 on the rated grades. The wide-temperature perimeter and low-closure-force source on this page. rogerscorp.com (BISCO silicones)
[12] Protective vent membrane data — W. L. Gore & Associates
Maker technical data for expanded-PTFE protective/breather vents for outdoor electronics enclosures: hydrophobic/oleophobic membrane, pressure equalization and condensation control, IP and IK impact ratings on the screw-in housings. The venting source on this page. gore.com (screw-in protective vents)
[13] PORON® microcellular urethane TDS — Rogers Corporation
Maker technical data for PORON® industrial microcellular polyurethane: service range about -40 to +90 °C, durable compression-set resistance, extra-soft to very-firm grades. The internal-cushion source on this page. rogerscorp.com (PORON industrial)
[14] Gasket compression & groove-design guidance
Engineering and vendor guidance on gasket compression percentage and groove design: roughly 15–25% compression for solid gaskets and 25–40% for hollow/sponge profiles, with groove depth set to hold the band. This is design consensus, not a mandated standard value; the achieved compression on the actual joint governs. stockwell.com (gasket compression)
Updated . Standards editions and links current at publication; verify against the publishing body before final spec. H-O converts materials tested to the methods cited; H-O does not certify enclosures. Lot-specific documentation available on request.
To review your outdoor enclosure sealing design, send:
- IP target (IP65 / IP66 / IP67)
- Any NEMA / UL Type requirement
- Enclosure construction (cast vs sheet-metal)
- Groove / land geometry
- Closure force or method
- Outdoor exposures (UV, salt fog, fuel)
- Operating & extreme temperature range
- Vent / condensation need + internal volume
- Gasket footprint drawing (DXF/STEP/PDF)
- Adhesive / liner requirements
- Prototype and annual volume
Get an outdoor-sealing engineering quote
Send a drawing, BOM, or enclosure spec. We typically respond within one business day with a material-and-vent recommendation, prototype lead time, and TDS verification against your IP target, environment, enclosure mechanics, and compression design.
See also: related H-O application pages
Engineering content for the adjacent Electronics & IoT sub-applications and the parent hub. Each page covers material selection, failure modes, and converter-side process detail for its application family.
Material data & standards. All durometer, temperature, compression-set, and immersion values on this page are taken from the source maker's technical data sheets and the cited standards (IEC 60529; NEMA 250; UL 50E; ASTM B117, D1149, G154/G155, D2240, D395, D1056, D471, D3574). IP, NEMA, and UL Type ratings are cited by designation: they evaluate the assembled enclosure, and the rating belongs to the tested unit, not to a gasket.
Gasket compression-percentage bands are qualitative engineering guidance; the achieved compression on the actual joint governs. H-O converts materials tested to these methods; H-O does not certify enclosures or independently certify materials against the standards unless explicitly stated on the quote. Verify against the maker TDS and the IP test on the assembled unit.
Conversion scope. H-O and converts sheet and roll stock to drawing in Winsted, Connecticut: die-cut and kiss-cut gaskets, CNC knife-cut gasket outlines and vent-membrane discs, slit strips, and multi-layer laminations, with material traceability and lot-code TDS records. H-O does not mold or extrude elastomers in-house; 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.