Custom Materials for Small (Non-EV) Lithium Battery Packs
H-O Products die-cuts and converts the thin parts that hold a small lithium pack together and keep it apart from itself: cell wraps and end insulators, pouch-cell compression pads, cylindrical-cell spacers, dielectric barriers between the cell stack and the BMS, thermal-runaway barrier layers, lid gaskets, and the kiss-cut adhesive that fixes each cell in place, built to your drawing.
Built for: 18650 and 21700 cylindrical packs and pouch-cell stacks in power tools, e-bikes and light electric vehicles, cordless and handheld devices, small backup and UPS-adjacent packs, medical devices, and IoT gateways, where compression, dielectric separation, and passive fire barriers are converted-part decisions and the pack safety listing belongs to the tested assembly.
To build the material set for a small (non-EV) lithium pack, work outward from the cell. Pouch cells: specify a PORON® microcellular urethane compression pad by its compression-force-deflection window per ASTM D3574 (an ultra-soft slow-rebound grade holds a light, near-constant force as the cell breathes ~5–10% over life). 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.
Pack- and cell-level, by designation (the listing belongs to the tested pack or cell): UL 2054 (household and commercial batteries) · UL 1642 (lithium batteries, cell level) · IEC 62133-2 (portable sealed secondary lithium cells and batteries) · UN 38.3 (transport tests T.1–T.8). Material- and enclosure-level, per the maker TDS: UL 94 (flammability classes incl.
V-0 on the rated grades) · ASTM D3574 (flexible cellular methods, microcellular urethane) · ASTM D2240 (durometer) · ASTM D149 (dielectric strength of the barrier films and papers) · IEC 60529 (ingress protection of the enclosure).
- Pouch compression pad: PORON® microcellular urethane
- Temperature / flame-class pad: BISCO® silicone foam
- Cell wrap / end insulator: PET/PVC sleeve + fish-paper rings
- Cylindrical spacer / keep-out: PE / EVA / PU foam
- Cell-to-BMS dielectric: Kapton® polyimide / PET / fish paper
- Thermal-runaway barrier: mica sheet / ceramic paper
- Lid gasket: EPDM / silicone foam
- Cell fixing / placement: acrylic transfer / foam PSA
This guide is for design and application engineers and procurement and sourcing buyers specifying wraps, compression pads, spacers, dielectric barriers, thermal-runaway barriers, lid gaskets, and adhesive-backed parts for small (non-EV) lithium battery packs in power tools, e-bikes and light electric vehicles, cordless and handheld devices, small backup packs, medical devices, and IoT hardware.
Pack layout & cell map → material selection → converted parts → production supply.
- 1Pack layout & cell mapCell format (18650, 21700, pouch), pack geometry, and where cells sit against each other, the BMS, and the housing.
- 2Requirement per layerPouch breathing budget and force, dielectric barrier locations, thermal-runaway barrier intent, lid closure force, and flame class.
- 3Choose the material familyMicrocellular urethane, silicone foam, EPDM, polyimide or PET film, fish paper, mica or ceramic paper, per the maker TDS.
- 4Add adhesive, liner & pull tabKiss-cut a PSA and liner where a part must place repeatably, with the bond validated on the actual surfaces.
- 5Die-cut to drawingDie-cut, kiss-cut, slit, and laminate each part to the cell footprint and the pack geometry.
- 6Quote prototype or productionPrototype kits through production runs, with material traceability and lot-code TDS records.
Where are you in the pack spec?
This page serves engineers who already know which converted part they need and engineers still assembling the material set layer by layer. Pick the path that matches where you are; you don't have to read the rest.
Send a drawing, get a quote
A cell wrap, a pouch compression pad in a named microcellular urethane grade, a dielectric barrier, a mica or ceramic layer, a lid gasket, or a complete pack material kit on your drawing.
Skip to the quote form →Build the material set requirement by requirement
Six selection factors (compression, dielectric separation, thermal-runaway barrier, wraps and spacers, lid sealing, cell fixing), a checklist-driven pack-layer builder, and nine material families with TDS-cited methods and by-designation standards language.
Start with selection factors →
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1Send drawingUpload a DXF, STEP, or PDF, or describe the pack, cell format, and layout. A sample part works too.
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2Material reviewEngineering reviews the pouch breathing budget, dielectric barrier locations, any thermal-runaway barrier intent, and the lid gasket against the maker TDSs, and frames the standards language correctly: material classes (UL 94) by TDS, pack and cell safety (UL 2054, UL 1642, IEC 62133-2, UN 38.3) by designation, with the listing belonging to the tested pack or cell.
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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 kiss-cut wrap and pad sets, and kitting for pack-level material kits. Ongoing parts run with material traceability and lot-code TDS records.
Which part of the pack are you building?
Application Zones
A small lithium pack is a stack of single-purpose converted layers. Seven of them recur across cylindrical and pouch designs: the wrap and end insulator that isolate each cell can, the compression pad that lets a pouch cell breathe, the spacer that holds cylindrical cells on pitch, the dielectric barrier between the cell stack and the BMS, the thermal-runaway barrier where the design calls for one, the lid gasket, and the kiss-cut adhesive that fixes cells in place.
Click a tab to see the part, the controlling property, and the families H-O converts for that zone.
Cell wraps & end insulators: isolate every can
On a bare cylindrical cell the can wall and the negative terminal sit at the same potential, so an unwrapped can that touches a neighbour, a busbar, or the housing is a short-circuit path. The barrel wrap, a PET or PVC heat-shrink sleeve, carries the can isolation, and a fish-paper or PET insulator ring sits over the positive end so the wrap edge and the busbar cannot bridge the terminal.
H-O the insulator rings, discs, and end-cap barriers to the cell footprint; the heat-shrink sleeve itself is an assembly item rather than a part. The same isolation logic applies to pouch tabs and to any place a conductor passes near a can edge.
Pouch-cell compression: let the cell breathe at constant force
A pouch cell changes volume roughly 5–10% as it charges, discharges, and ages, and it must not be boxed in with nowhere to go. The compression pad between adjacent pouch cells (or between a pouch cell and a rigid wall) is a spring: it holds a light, near-constant force across that swing and across the pack's multi-year life. PORON® microcellular urethane is the family, because its defining property is low compression set: the force window survives years of cycling rather than relaxing away.
This is the same pouch-compression discipline the EV pack pages carry, scaled to one small pack; the pad is specified by its compression-force-deflection curve (per ASTM D3574 on the TDS), not by thickness. Where a temperature or flame class governs, BISCO® cellular silicone takes the same role with UL 94 listings per the grade TDS.
Cylindrical spacers & holders: hold cells on pitch
18650 and 21700 cells want to sit on pitch, air-gapped from one another, and off the housing wall. The moulded plastic cell holder that sets the array is a partner-network form; the converted parts are the foam and film spacers, keep-outs, and insulator sheets that fill the gaps the holder leaves, cushion the array against the housing, and keep a can off a sharp structural edge.
Crosslinked-PE, EVA, and PU foams cover the light-duty cushioning, and thin PET or fish paper handles the places a spacer also has to insulate. Send the cell map and the keep-out zones; the spacer set falls out of the array geometry.
Cell-to-BMS dielectric: keep the stack off the board
The busbars, nickel strip, and cell terminals sit at pack voltage millimetres from the BMS traces and pads. A dielectric barrier between the cell stack and the board carries the isolation, and barrier washers isolate individual standoffs and fastener heads. The split is by mechanics and temperature: Kapton® polyimide film where the barrier must be thin and take heat, PET film where cost and thickness suit, and fish paper / vulcanized fibre where a traditional conformable insulating paper fits the joint.
Creepage and clearance decisions follow the pack design; the films and papers here are the materials those decisions get built from, with dielectric strength per the grade TDS.
Thermal-runaway barrier: passive layers between cells
Where the pack design calls for a passive thermal-runaway layer, a mica sheet or ceramic / refractory paper goes between cells or over cell vents to slow heat and hot-particle propagation from a cell in runaway. Mica is the classic choice: inorganic, thin, and stable at flame temperatures, with phlogopite favoured for higher-temperature stability and muscovite for higher dielectric strength (per the grade TDS).
Ceramic / refractory paper (alumina-silica nonwoven) is a lightweight alternative, with UL 94 V-0 grades available per the maker TDS. One sentence governs this zone: the barrier is an ingredient of a design whose thermal-runaway behaviour is evaluated on the tested pack, and any listing belongs to that pack, cited here by designation.
Lid gasket & cell fixing: seal it, fix it
Two ordinary jobs close the pack. The lid gasket, a EPDM or silicone foam run around the enclosure seam, excludes dust and moisture; the IP rating is earned by the assembled enclosure per IEC 60529, not by the foam alone, so match the gasket's compression class to the real closure force and let any flame-class requirement pick between the EPDM and silicone tracks.
Cell fixing is the other: a kiss-cut acrylic transfer or foam adhesive on a liner (with a pull tab) fixes each cell or part in position so assembly can place it to the drawing repeatably. Any adhesive choice is validated on the actual surfaces: the bond depends on the substrate, its surface energy, temperature, exposure, dwell, pressure, prep, geometry, and how the assembly comes together, so H-O frames the tape as a candidate to qualify, not a finished result.
Six decisions that drive your small-pack material spec
A small pack is a stack of single-purpose converted layers, and each layer has one controlling property. Miss one and the failure is rarely immediate: a compression pad relaxes, a barrier is in the wrong place, a wrap edge bridges a terminal, or a safety review stalls on a material nobody can document.
Materials carry classes; packs carry listings. UL 94 V-0 belongs to a material grade per its TDS. UL 2054, UL 1642, IEC 62133-2, and UN 38.3 belong to the tested pack or cell. Write material classes on the part callouts, cite pack and cell safety by designation, and never let a drawing imply that a barrier is "UL 2054 certified": the barrier supports a pack evaluated to it.
A pouch cell breathes as it charges, discharges, and ages. The pad has to absorb that swing while holding a light, near-constant force for the pack's whole life. That is a compression-force-deflection decision, not a thickness decision, and the family that holds the window over years is the one with the lowest compression set.
Read the six factors below in order. The first two build the electrical core (compression, dielectric separation); the next two add the safety and structural layers (thermal-runaway barrier, wraps and spacers); the last two close the pack (lid sealing, cell fixing). Every factor names its test method, because in this application the documentation is part of the part.
Show all 6 selection factors tap to expand
Pouch compression: specify the force window, not the thickness
Rule — get the cell maker's target force and the breathing budget onto the drawing, then let the compression-force-deflection curve pick the grade and thickness. A pouch cell breathes ~5–10% over life and must not be over-constrained; the pad is a spring specified by its CFD window, not its gauge.
PORON® microcellular urethane holds the family's defining property, low compression set, so the light preload survives years of cycling; methods are per ASTM D3574 on the TDS, and a flame-rated grade adds a UL 94 class where the location demands it. [5]
Dielectric separation: thin film where it bends, paper where it conforms
Rule — name the barrier film gauge or paper designation and where each one lives, and keep spacing decisions inside the pack's creepage/clearance practice. Insulation has to follow busbars, wrap cells, and stand between the cell stack and the BMS in tight spaces.
The split is by mechanics and temperature: Kapton® polyimide film where the barrier is thin and takes heat, PET film where cost and thickness suit, and fish paper / vulcanized fibre where a conformable insulating paper fits the joint. The maker TDSs carry the dielectric methods (ASTM D149-class). [7]
Thermal-runaway barrier: name the tier, cite the pack
Rule — decide early whether the design carries a passive barrier and draw it as a part; retrofitting a fire layer into a finished pack is the expensive version of the same spec. Where the design calls for one, a mica sheet (phlogopite for temperature, muscovite for dielectric strength) or ceramic / refractory paper goes between cells or over vents to slow propagation.
The barrier is an ingredient of a strategy evaluated on the tested pack per UL 2054 / IEC 62133-2; write the standards language so the material supports the design and the listing belongs to the pack. [1]
Wraps & spacers: isolate every can, hold every pitch
Rule — treat the cell can as a live surface and design the isolation as parts. On a cylindrical cell the can is at negative potential, so the barrel wrap (PET/PVC sleeve) plus a fish-paper or PET insulator ring over the positive end keeps the wrap edge and busbar from bridging the terminal. Die-cut foam and film spacers hold 18650/21700 cells on pitch, air-gapped, and off the housing wall. Send the cell map and the keep-out zones; the wrap, ring, and spacer set falls out of the array geometry.
Lid sealing: ordinary gasket, real ingress stakes
Rule — match the gasket's compression class to the real closure force, and let any flame-class requirement pick the EPDM or silicone track before cost does. The lid gasket is specified like any enclosure seal (closure force, gap, compression class per ASTM D1056), but the IP rating is earned by the assembled enclosure per IEC 60529, not by the foam alone. EPDM foam is the economical default; BISCO® cellular silicone steps in where temperature endurance or a UL 94 flame class drives the choice, with listings per the grade TDS. [8]
Cell fixing: place it repeatably, validate the bond
Rule — kiss-cut a PSA and liner with a pull tab so assembly places each cell or part to the drawing, and qualify the adhesive on the real surfaces. Bond performance depends on the substrate, its surface energy, temperature, exposure, dwell, pressure, prep, geometry, and how the assembly comes together, so the adhesive is a candidate to validate, not a finished result. Acrylic transfer and foam adhesives, including low-surface-energy grades for slick wraps and housings, cover the range; the liner and pull tab make each part placeable.
Specification Tools
Two tools to take you from "we're building a small pack" to here's the material checklist for the drawing set: a requirement-driven pack material builder that assembles the layer list with its citations, and a side-by-side comparison of every pack-side family on this page.
1. Small-pack material checklist builder
Check the requirements your pack carries. The builder assembles the corresponding converted layers into a checklist with the family, what to send with the drawing, and the citation language (material classes per TDS; pack and cell safety by designation, the listing with the tested pack or cell). The default selection is pre-built for a typical pouch-cell pack; every layer is also printed in the material reference section, so nothing here exists only behind a script.
Material checklist: 4 layers selected
Each checked requirement adds its layer below. The list is the starting bill of materials for the engineering review, not a certification: material classes (UL 94) come from the grade TDS, and pack and cell safety (UL 2054 / UL 1642 / IEC 62133-2 / UN 38.3) are cited by designation with the listing belonging to the tested pack or cell.
- Pouch compression pad: PORON® microcellular urethane (flame-rated grade for V-0 duty)Send: cell breathing budget (%), target force, pad footprint. Cite: ASTM D3574 methods; UL 94 class per the grade TDS.
- Cell wrap / end insulator: PET/PVC sleeve + fish-paper ringsSend: cell format, terminal geometry, wrap-edge clearance. Cite: dielectric methods per the grade TDS.
- Cell-to-BMS dielectric: Kapton® polyimide / PET / fish-paper barrierSend: board outline, barrier locations, creepage/clearance need. Cite: dielectric strength per the maker TDS (ASTM D149-class).
- Lid sealing: EPDM foam or silicone-foam gasketSend: closure force, gap, flame-class requirement, IP target. Cite: ASTM D1056 classes; IP at the enclosure per IEC 60529.
2. Side-by-side: pack-side 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 zone 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 | Zone | |
|---|---|---|---|---|---|
| The electrical core (compression & dielectric) | |||||
| PORON® Microcellular Urethane (4701 / 4790 Series)Microcellular urethane | Microcellular PU foam | Compression window (CFD) | ASTM D3574; UL 94 per grade TDS | Pouch compression | |
| BISCO® Silicone Foam (HT / BF) + V-0 SpongeCellular silicone | Closed-cell silicone | Temperature / flame class | UL 94 (per grade TDS); ASTM D1056 | Compression / lid | |
| PE / EVA / PU Foam CushionLight-duty foam | Crosslinked-PE / EVA / PU | Take-up / cushion | ASTM D3574 (per TDSs) | Spacers / cushion | |
| Kapton® Polyimide FilmPolyimide film | Thin dielectric film | Dielectric strength / gauge | ASTM D149 (per TDS) | Cell-to-BMS | |
| PET Film Barrier / InsulatorPolyester film | Die-cut PET film | Dielectric / thickness | ASTM D149 (per TDS) | Barriers / spacers | |
| Fish Paper / Vulcanized Fibre + Nomex® 410Insulating papers | Die-cut dielectric paper | Conformable dielectric | Per grade TDS | Wraps / barriers | |
| The safety & closure layers | |||||
| Mica Barrier Sheet (Phlogopite / Muscovite)Inorganic barrier | Mica laminate sheet | Barrier tier (cell-to-cell) | Supports UL 2054 / IEC 62133-2 designs (by designation) | Thermal-runaway | |
| Ceramic / Refractory + Glass-Fibre PaperHigh-temp papers | Alumina-silica / glass nonwoven | Barrier / high-temp interleave | UL 94 V-0 (per grade TDS) | Thermal-runaway | |
| EPDM Foam + Kiss-Cut Acrylic PSALid seal & fixing | Closed-cell EPDM / acrylic PSA | Compression class / bond duty | ASTM D1056; IEC 60529 (enclosure) | Lid & fixing | |
Skip ahead and request your engineering review now
If your drawing set already calls out a compression pad grade, a dielectric barrier, a mica or ceramic layer, or a lid gasket construction, send it over for engineering review against the TDSs and the standards language.
Small-pack material failures you can prevent at spec
Small packs fail quietly first: a preload that relaxed, a wrap edge that bridged a terminal, a barrier that was never drawn, a lid seal that opened, a safety review that stalled on an undocumented layer. Six patterns cover most of what goes wrong, and each is a specification decision made before the first part is cut.
In battery packs, the paperwork is part of the part. A correct material with an undocumented class, or a drawing that claims a pack listing for a component, costs more schedule at review than any cutting error. Cite material classes per TDS and pack and cell safety by designation.
Show all 6 failure modes tap to expand
1. A pouch pad specified by thickness, and the preload quietly expired
A compression pad was picked by gap fill: the right thickness on day one, the wrong spring forever.
As the pouch cell breathes and ages, a pad chosen without its compression-force-deflection curve drifts out of the target force window, internal layer contact degrades, and capacity or swelling complaints follow months later. Fix — specify the force window, not the gauge: state the target force and the breathing budget, and pick the microcellular-urethane grade whose ASTM D3574 CFD data holds that window across the deflection span; the family's low compression set is what keeps the spec alive over the years.
2. A bare or nicked cell can that shorted to its neighbour
On a cylindrical cell the can wall is at negative potential, so a missing wrap, a nicked sleeve, or a wrap edge that crept over the positive end let the can bridge a neighbour, a busbar, or the housing, a short-circuit path that shows up as a dead cell or worse. Fix — design the isolation as parts: an intact PET/PVC barrel sleeve plus a fish-paper or PET insulator ring over the positive terminal, cut to the cell footprint so the wrap edge and the busbar cannot meet.
Die-cut rings with accurate, sealed edges remove the hand-trimming that starts most of these shorts.
3. The cell-to-BMS barrier that fit the voltage but not the geometry
The barrier was there, but a busbar edge creased a thin film, a fish-paper sheet slipped off a standoff, or a clearance that looked generous on paper disappeared behind a service loop, and a terminal found a BMS trace.
The failure is mechanical, not electrical: films wrinkle and tear at radii, papers migrate if they are not located. Fix — split the dielectric jobs by mechanics: Kapton® film where the barrier bends, PET where thickness and cost suit, fish paper where a conformable paper fits, each with locating features and sealed edges, and keep spacing decisions inside the pack's creepage/clearance practice.
4. The thermal-runaway barrier that was never drawn (or claimed the wrong credit)
Two versions of one failure. In the first, passive propagation containment was assumed to live somewhere else, and the pack design closed without a barrier tier; adding mica or ceramic paper after the geometry is frozen is the expensive retrofit. In the second, a drawing note claims "UL 2054 barrier" for a sheet, and the review stalls, because UL 2054 evaluates the tested pack, not a material.
Fix — decide the barrier tier early, draw it as a part, and write the standards language correctly: the material supports a design evaluated per UL 2054 / IEC 62133-2; the listing belongs to the pack. [1]
5. A lid seal that opened, and the ingress rating that never held
The gasket looked fine, but it was sized by cross-section rather than by closure force, so it either over-compressed and took a set or never compressed into its working range, and dust and moisture found the seam.
Or the design leaned on the foam for the IP rating the assembled enclosure never earned. Fix — match the gasket's compression class (per ASTM D1056) to the real closure force, let any flame-class requirement pick the EPDM or silicone track, and treat the IP rating as an enclosure-level result validated per IEC 60529, not a property of the gasket alone.
6. A cell that migrated, because the adhesive was assumed rather than validated
Cells shifted under vibration, abraded their wraps, and stressed the welds, because the fixing adhesive was chosen on a datasheet number and never qualified on the actual wrap and housing surfaces.
Slick, low-surface-energy wraps and housings are exactly where an unvalidated bond lets go. Fix — kiss-cut the PSA and liner so assembly places each cell to the drawing, and qualify the adhesive on the real substrate, surface energy, temperature, exposure, dwell, pressure, prep, geometry, and assembly, reaching for a low-surface-energy acrylic where the surface demands it.
The bond is a candidate to validate, not a finished result.
Material reference
Detailed specs for the nine pack-side families referenced on this page: the compression set (PORON® microcellular urethane, BISCO® silicone foam, and the light-duty foams), the dielectric set (Kapton® polyimide, PET film, and the insulating papers), and the safety and closure set (mica and ceramic/glass barrier papers; EPDM lid gaskets and kiss-cut acrylic adhesives).
Values are per the maker TDS on file for each grade with the method named; pack and cell safety standards are cited by designation only, with the listing belonging to the tested pack or cell.
H-O die-cuts, kiss-cuts, slits, and kits every family to drawing.
PORON® Microcellular Urethane (4701 / 4790 Series)Pouch compression pads · ASTM D3574 methods · low compression set
Specify the force window and breathing budget, not just thickness. The EV pouch-compression playbook applies directly at small-pack scale; the EV & battery pages carry the deep version for mobile platforms.
BISCO® Silicone Foam (HT / BF Series) & V-0 Silicone SpongeTemperature / flame-class pads & gaskets · UL 94 per grade TDS
Let the flame-class requirement pick the silicone track before cost does; UL 94 listings are per the individual grade TDS.
PE / EVA / PU Foam Cushions & SpacersLight-duty cushion & spacers · ASTM D3574 per TDS
Step up to the microcellular-urethane pad wherever the joint needs a specified, stable force window over life.
Kapton® Polyimide FilmCell-to-BMS dielectric barrier · thin, high-temperature · ASTM D149 per TDS
Choose gauge to the wrap radius and the standoff geometry; the maker TDS carries the dielectric method.
PET Film Barrier / InsulatorEconomical dielectric barrier & spacer film · ASTM D149 per TDS
Where a PET grade is not called out by a dedicated family, the umbrella films-papers-laminates line covers it; name the grade on the drawing.
Fish Paper / Vulcanized Fibre & Nomex® 410 Aramid PaperConformable dielectric papers · per grade TDS
Fish paper / vulcanized fibre is specified in plain text against the films-papers-laminates umbrella; name the paper on the drawing.
Mica Barrier Sheet (Phlogopite / Muscovite)Thermal-runaway & dielectric barrier · supports UL 2054 / IEC 62133-2 designs
Cautious language is part of this material's spec: the barrier supports a thermal-runaway strategy that is evaluated on the tested pack. H-O supplies the converted layer and its documentation; the pack designer owns the evaluation.
AeroZero® Polyimide-Aerogel Film & Flame Barrier (Blueshift)Ultra-thin thermal-runaway & flame barrier film · UL 94 VTM-0 per grade TDS
- AZ-TPS 100 · AZ-TPS 101 single- and double-sided silicone-PSA aerogel film, 190–216 µm, UL 94 VTM-0
- AZ-TPS PI 100 polyimide-faced aerogel film, 240 µm, UL 94 VTM-0 — durable outer skin for handling and wear
- TripleZero TPS 300 three-layer aerogel laminate, 570 µm, UL 94 V-0 — passes the FAR 25 Appendix F 12-second vertical burn per manufacturer data
- QuinZero TPS 501 five-layer laminate with acrylic interlayers, 953 µm — maximum thermal resistance per part; acrylic interlayers limit service temperature vs. silicone grades, verify on the TDS
Ceramic / Refractory Paper & Glass-Fibre Paper (ManniGlas®)Lightweight high-temperature barrier papers · UL 94 V-0 per grade TDS
As with mica, the barrier supports a pack-level design; the thermal-runaway performance and any listing belong to the tested pack.
EPDM Lid Gaskets & Kiss-Cut Acrylic AdhesivesLid seal & cell fixing · ASTM D1056 · IP at the enclosure (IEC 60529)
Match the gasket compression class to the real closure force; qualify the fixing adhesive on the real wrap and housing surfaces before committing the bond.
Small battery-pack materials: engineer-grade FAQ
Eleven of the questions we hear most from power-tool, e-bike, portable, medical, and IoT pack teams. If your question isn't here, send a drawing or call, engineering picks up.
Does H-O certify a pack to UL 2054, IEC 62133, or UN 38.3?
No, and no honest supplier will claim otherwise: UL 2054 (household and commercial batteries), UL 1642 (lithium cells), IEC 62133-2 (portable sealed secondary lithium cells and batteries), and UN 38.3 (transport tests) evaluate the tested pack or cell, so the listing belongs to that assembly. What the converted materials carry is their own documentation: material-level classes like UL 94 on the rated grade TDSs, the test methods behind their properties, and lot-code traceability.
They support designs evaluated to the pack and cell standards; H-O supplies the layers and the paperwork, and the pack designer owns the evaluation. [1]
What is the difference between UL 1642 and UL 2054?
Different tiers. UL 1642 is the cell-level lithium-battery safety standard; it evaluates the cell. UL 2054 is the pack/battery-level standard for household and commercial batteries; it evaluates the complete unit, including the protection circuit, connectors, and housing, and it builds on cell-level results. IEC 62133-2 is the international counterpart covering portable sealed secondary lithium cells and the batteries made from them.
All are cited by designation on this page; the converted materials are ingredients of a design evaluated to them. [2]
What compression pad goes between pouch cells?
A microcellular urethane pad (PORON® class) sized by its compression-force-deflection window per ASTM D3574, not by thickness. A pouch cell breathes as it charges and ages, and the pad has to hold a light, near-constant force across that swing for the pack's whole life; the family's low compression set is what keeps the force window valid over the years. A slow-rebound extra-soft grade suits a gently breathing pouch; step to BISCO® silicone foam where a temperature or flame class governs. [5]
How much do pouch cells swell, and why does it matter?
A pouch cell changes volume on the order of 5–10% as it charges, discharges, and ages, and it must not be boxed in with nowhere to expand. That is why the compression pad is compressible and specified by force rather than gauge: it absorbs the swelling while holding the cell at a controlled, near-constant force. Restricting a pouch cell with no room to breathe damages it; a pad chosen only by thickness relaxes and stops holding force. Send the breathing budget with the drawing.
What goes between the cells and the BMS?
A dielectric barrier: Kapton® polyimide film where the barrier must be thin and take heat, PET film where thickness and cost suit, or fish paper / vulcanized fibre where a conformable insulating paper fits the joint. It keeps the busbars, nickel strip, and cell terminals off the BMS traces and pads, and barrier washers isolate individual standoffs and fastener heads. Creepage and clearance follow the pack design; dielectric strength is per the grade TDS. [7]
PET vs polyimide vs fish paper: which dielectric barrier?
By mechanics and temperature. Kapton® polyimide is the thin, high-temperature, high-dielectric-strength choice where space is tight or heat is present. PET film is the economical barrier where thickness and cost suit and temperatures are moderate. Fish paper / vulcanized fibre is the conformable insulating paper for interleaves, insulator rings, and places a paper drapes better than a film; Nomex® 410 aramid paper steps in where the paper runs warm. All are to the geometry with sealed edges; the grade TDS carries the dielectric method. [7]
Does a small pack need a mica or ceramic thermal-runaway barrier?
It depends on the pack's safety design, and that call belongs to the system, not to a converted material. Where the design calls for a passive propagation barrier, a mica sheet (phlogopite for temperature, muscovite for dielectric strength) or a ceramic / refractory paper goes between cells or over vents to slow heat and hot-particle spread.
The material supports a strategy that is evaluated on the tested pack per UL 2054 / IEC 62133-2; the barrier does not carry the listing, the pack does. Decide the tier early so it can be drawn as a part. [1]
How are cylindrical cells wrapped and insulated?
Two parts. The barrel wrap is a PET or PVC heat-shrink sleeve that isolates the can, which sits at negative potential; that sleeve is an assembly item rather than a part. Over the positive end, a fish-paper or PET insulator ring keeps the wrap edge and the busbar from bridging the terminal. H-O the insulator rings, discs, and end-cap barriers to the cell footprint; send the cell format and the terminal geometry.
Can H-O kiss-cut a PSA to fix cells in place?
Yes: acrylic transfer and foam adhesives can be kiss-cut on a liner with a pull tab so assembly places each cell or part to the drawing repeatably, including low-surface-energy grades for slick wraps and housings. The bond is validated on the actual surfaces: it depends on the substrate, its surface energy, temperature, exposure, dwell, pressure, prep, geometry, and how the assembly comes together, so H-O frames the adhesive as a candidate to qualify against your duty, not a finished result.
What lid gasket seals an IP-rated pack?
A EPDM foam gasket is the economical default, with a compression class per ASTM D1056 matched to the real closure force; move to silicone foam where temperature endurance or a UL 94 flame class drives the joint. Either way the IP code is earned by the assembled enclosure per IEC 60529, not by the foam alone, so the gasket is one variable in an enclosure-level result. Send the closure force, the gap, the flame-class requirement, and the IP target. [8]
What should I put on the drawing so the quote comes back right the first time?
By layer: for the compression pad, the pouch breathing budget and target force; for the wraps and spacers, the cell format and the keep-out zones; for the dielectric barrier, the board outline, barrier locations, and any creepage/clearance requirement; for the thermal-runaway barrier, the tier intent and the pack it supports; for the lid, the closure force, gap, flame class, and IP target; for cell fixing, the wrap and housing surfaces.
Plus quantities for prototype and production, and the standards language you need on the paperwork (material classes per TDS; pack and cell safety by designation). "Recommend the material set" is a valid callout: that is what the engineering review is for.
Glossary: terms used on this page
Quick reference for the small-pack battery terminology used throughout. Each entry links to the relevant standard or test method where applicable.
UL 2054 (by designation)
The standard for household and commercial batteries: the pack/battery tier of the safety chain, per [1]. It evaluates the complete pack, not its component materials; on this page it is cited by designation, and the materials support designs evaluated to it.
UL 1642 & IEC 62133-2 (by designation)
UL 1642 is the cell-level lithium-battery safety standard; IEC 62133-2 [3] covers portable sealed secondary lithium cells and the batteries made from them. Both attach to the tested cell or battery. Converted materials are ingredients of a design evaluated to them, never holders of the result.
UN 38.3 (by designation)
The transport-test sub-section of the UN Manual of Tests and Criteria: the T.1–T.8 series (altitude, thermal, vibration, shock, external short circuit, impact/crush, overcharge, forced discharge) a lithium cell or battery passes to ship, per [4]. Cited by designation as transport context.
Compression force deflection (CFD)
The force a cellular material exerts at a given compression, the curve that turns a foam pad into a specifiable spring. Reported per ASTM D3574 [5] on the microcellular-urethane TDSs; pouch compression pads are specified by their CFD window, not their thickness.
Compression set
Permanent thickness lost after sustained compression, reported per ASTM D3574 [5]. The property that decides whether a pouch pad's light preload window is still valid years later; the microcellular-urethane family is chosen for its low value.
Pouch cell breathing / swelling
The cyclic and long-term volume change of a lithium pouch cell as it charges, discharges, and ages, on the order of 5–10% [9]. The compression pad absorbs this swing while holding a controlled force; a cell restricted with no room to breathe is damaged.
Fish paper / vulcanized fibre
A traditional die-cuttable dielectric insulating paper (vulcanized cellulose fibre), used for cylindrical-cell insulator rings, end-cap barriers, interleaves, and cell-stack-to-BMS barriers. Conformable and easily cut to drawing; dielectric properties per the grade TDS.
Mica (phlogopite / muscovite)
An inorganic, thin, high-temperature dielectric and fire-barrier material, laminated into sheet, used between cells or over vents as a passive thermal-runaway barrier. Phlogopite favours higher-temperature stability, muscovite higher dielectric strength [10]; barrier performance belongs to the tested pack.
BMS (battery management system)
The board that monitors and protects a lithium pack (cell balancing, overcurrent, over/under-voltage, temperature). It sits millimetres from the cell terminals and busbars, which is why a dielectric barrier separates the two.
IP rating (IEC 60529)
The ingress-protection code (dust and water), defined by IEC 60529 [8]. Earned at the assembled-enclosure level; the lid gasket is one variable in that result, not the rating itself.
Listing belongs to the tested pack
The honesty rule for standards claims: pack and cell safety standards attach to the evaluated pack or cell, not its component materials; a material carries its own classes and supports a listed design without inheriting its listing.
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. Pack and cell safety standards are cited by designation: they evaluate packs and cells, and the listing belongs to the tested assembly. Standards editions current as of July 2026; verify against the publishing body before final spec. H-O materials are aligned to these standards through the source manufacturer's TDS, not independently certified by H-O unless explicitly stated on the quote.
[1] UL 2054 (by designation)
Standard for Household and Commercial Batteries. The pack/battery-level safety standard that evaluates the complete unit, building on cell-level results. Cited by designation; the listing belongs to the tested pack. shopulstandards.com (UL 2054)
[2] UL 1642 (by designation)
Standard for Lithium Batteries. The cell-level safety standard for primary and secondary lithium cells; the foundation UL 2054 builds on. Cited by designation; the listing belongs to the tested cell. shopulstandards.com (UL 1642)
[3] IEC 62133-2 (by designation)
Secondary cells and batteries containing alkaline or other non-acid electrolytes — Safety requirements for portable sealed secondary cells and batteries — Part 2: Lithium systems. Vibration and mechanical-shock content is aligned with UN 38.3. Cited by designation. webstore.iec.ch (IEC 62133-2)
[4] UN 38.3 (by designation)
UN Manual of Tests and Criteria, sub-section 38.3 — Lithium metal and lithium-ion batteries transport tests T.1–T.8 (altitude, thermal, vibration, shock, external short, impact/crush, overcharge, forced discharge). Cited by designation as transport context. unece.org (Manual of Tests and Criteria)
[5] ASTM D3574
Standard Test Methods for Flexible Cellular Materials — Slab, Bonded, and Molded Urethane Foams (density, compression-force-deflection, compression set). The material-level method behind the compression pad's force window. astm.org (ASTM D3574)
[6] UL 94
Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances (HB, HBF, HF-1, V-0 classes). Material-level flammability classes are per the individual grade TDS. shopulstandards.com (UL 94)
[7] ASTM D149
Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies. The dielectric-strength method behind the barrier films and papers, per the grade TDS. astm.org (ASTM D149)
[8] IEC 60529 (by designation)
Degrees of protection provided by enclosures (IP Code). The ingress rating is earned at the assembled-enclosure level; the lid gasket is one variable in that result. webstore.iec.ch (IEC 60529)
[9] Pouch-cell battery-pad design (maker application note)
Application note on designing a compression pad for lithium pouch cells: the ~5–10% cell breathing, the need for a light, consistent force across a wide compression range, and compression-set resistance over an 8–10 year life. Basis for the pouch-compression discipline on this page. stockwell.com (pouch battery pad)
[10] Mica battery-safety barrier TDS (maker)
Mica insulation for battery safety: inorganic high-temperature dielectric and thermal-runaway barrier; phlogopite for higher-temperature stability, muscovite for higher dielectric strength. Barrier performance belongs to the tested pack. elmelin.com (mica battery safety)
[11] Microcellular polyurethane (PORON) TDS (maker)
PORON® microcellular polyurethane product family and data sheets (4701 series cushion; 4790 slow-rebound extra-soft): low compression set, consistent force over a wide compression range, vibration/shock damping, low outgassing. rogerscorp.com (PORON industrial)
[12] Ceramic-fibre / refractory paper barrier (maker)
Ceramic-fibre (alumina-silica) refractory papers and battery fire-barrier materials for lithium packs: lightweight high-temperature barrier papers, with UL 94 V-0 grades per the maker TDS. Barrier performance belongs to the tested pack. unifrax.com (battery barrier papers)
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 packs or cells. Lot-specific documentation available on request.
To review your small-pack material set, send:
- Cell format (18650, 21700, pouch)
- Pack layout / cell map / board outline
- Pouch breathing budget and target force
- Dielectric barrier locations
- Any creepage / clearance requirement
- Thermal-runaway barrier intent
- Lid closure force, gap & IP target
- Flame-class requirement
- Adhesive / liner / pull-tab needs
- Prototype and annual volume
Get a small-pack materials engineering quote
Send a drawing set, cell map, or pack spec. We typically respond within one business day with a material-set recommendation, prototype lead time, and TDS verification against your compression window, dielectric barriers, thermal-runaway barrier intent, lid seal, and standards language.
See also: related H-O application pages
Engineering content for the adjacent Electronics & IoT and EV battery 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
Display, PCB & shock protection
The board-and-display half of the same devices: cushion gaskets, board-level shock pads, standoff washers, and kiss-cut PSA parts.
Read the page
Sibling sub-application
Enclosure sealing & IP protection
The full enclosure-sealing playbook behind this page's lid gasket: perimeter gaskets, compression classes, and IP earned at the enclosure.
Read the page
Sibling sub-application
Electrical insulation & dielectric
The deep dielectric-barrier playbook behind this page's cell-to-BMS layer: polyimide, PET, fish paper, and creepage/clearance.
Read the page
EV counterpart
EV battery compression & cushioning
The EV-pack-scale version of this page's pouch-compression discipline: PORON compression pads specified by force window across cell breathing.
Read the page
Industry hub
Electronics & IoT
The full Electronics & IoT application family: enclosure sealing, EMI shielding, thermal management, dielectric insulation, and small battery packs.
Read the page
Material data & standards. All compression, dielectric, and temperature values on this page are taken from the source maker's technical data sheets with the method named (ASTM D3574, D2240, D149; ASTM D1056; UL 94 classes per the listed grade TDSs).
Pack and cell safety standards (UL 2054, UL 1642, IEC 62133-2, UN 38.3) and IEC 60529 ingress protection are cited by designation only: they evaluate packs, cells, and enclosures, the listing belongs to the tested assembly, and the materials on this page support designs evaluated to them.
H-O converts materials; H-O does not manufacture cells, design battery systems, or certify packs, and does not independently certify materials against the standards unless explicitly stated on the quote. Verify against the maker TDS and your pack-level evaluation plan.
Conversion scope. H-O and converts sheet, roll, and blanket stock to drawing in Winsted, Connecticut: die-cut and kiss-cut pads, wraps, barriers, and gaskets, slit films, laminations, and kitted pack sets, with material traceability and lot-code TDS records. H-O and converts; molded cell holders and extruded profiles are outside that scope and are coordinated through a partner network (typical 4–6 week tooling lead times). Lead-time and MOQ details are in the process strip and the quote form above.