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How to Spec an EV Cell Compression Pad: What to Send H-O for a Quote
A compression-pad RFQ moves at the speed of its slowest missing number. Send a footprint sketch alone and the first response is a list of questions; send the eight items below and the first response is a material direction, a grade and thickness proposal, and a quote. This article is the checklist the H-O applications engineering team works from when a cell-stack pad request arrives, what each item is, why it changes the answer, and what happens after you hit send.
It is written for pouch and prismatic stack designers; cylindrical cells are generally self-constraining and rarely need this part.
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The eight things to send, and why each one matters
| Send this | Why engineering needs it |
|---|---|
| 1. Cell format and thickness | Pouch or prismatic, and the nominal cell thickness. Pouch cells rely on external compression for electrode-stack stability; prismatic cells are stiffer but still benefit from controlled pressure. The format frames every later number. |
| 2. Beginning-of-life (BOL) gap | The as-built space the pad fills sets the initial deflection, the first point that must land on the flat region of the compression-force-deflection (CFD) curve. |
| 3. Expected breathing percentage | The reversible per-cycle thickness change the pad must flex with. It defines the small oscillation the working point makes around its place on the plateau. |
| 4. Expected end-of-life swelling percentage | Cells commonly run about 10 to 20% thicker at end of life. This one-way growth defines the deepest deflection the pad will ever see, the second point that must stay on the plateau and out of densification. |
| 5. Target pressure window | From your cell supplier's guidance. Research supports light-to-moderate preload helping life while over-compression may accelerate aging, and the right window is chemistry- and format-specific, so we work from your cell maker's number, never a generic one. |
| 6. Pad footprint drawing | Outline, cut-outs, and tolerances. The footprint drives die selection (steel-rule die, kiss-cut, laser, waterjet), nesting, and price; cut-outs near edges can change the cutting method. |
| 7. Adhesive / liner requirements | Whether the pad must self-locate during module assembly (PSA one side, two sides, or none), and how the line wants it presented: kiss-cut on a roll, sheets, pull-tabs. |
| 8. Prototype and annual volume | Quantity shapes the converting plan and the price break structure. Prototype quantities and full production runs are equally accepted; the method may differ (tooling-free laser for first articles, production dies at volume). |
What the numbers decide, in order
The review follows the same sequence the parent application page teaches. The pressure window and deflection range come first, because they decide whether the part is even a compression pad rather than a gap filler.
The family comes second: PORON microcellular polyurethane (including the PORON EVExtend battery grades) leads on plateau flatness and low compression set across normal module temperatures; BISCO closed-cell silicone foam takes over where continuous temperature or a UL 94 flame class governs, with V-0 available on specific grades, and a dedicated V-0 silicone sponge covers parts where the flame listing leads outright.
Grade and thickness come last, placed so the BOL and EOL deflections both sit on the flat CFD region (per ASTM D3574 Test C / ISO 3386), with compression set and stress relaxation (ASTM D395 / D3574; ASTM D6147 / ISO 3384) checked at your temperature.
Two cautions save revision loops. First, specify the curve, not a durometer: two foams of similar firmness age differently, and the data-sheet CFD curve plus set value is the real spec. Second, if the same layer must also do a thermal job, say so explicitly; a pad and a gap filler are opposite materials, and a dual-duty slot needs a reviewed stack-up rather than a compromise foam.
What happens after you send it
- Drawing review. An applications engineer reads the stack drawing against the eight items, typically the same business day, and comes back with either a material direction or the specific missing numbers.
- Material direction and quote. A family, grade direction, and thickness proposal, with the TDS attached, plus converting method, presentation, and pricing at your quantities.
- Samples. Die-cut samples typically ship in 3 to 5 business days for common configurations on materials on hand, so the stack can be validated physically before tooling.
- Production. Standard production runs about two weeks after drawing approval; special orders are quoted to the job. MOQ varies by material and part; prototype quantities through full production runs are equally accepted.
Documentation available with the part
Material technical data sheet, certificate of conformance, lot traceability, and first-article inspection are available on request, produced under our ISO 9001:2015 certified quality management system. Note the boundary honestly: H-O converts the pad and documents the converting; grade-level properties (CFD, set, relaxation, UL 94 class) are the manufacturer's published data, and pack-level outcomes such as UN 38.3 transport testing or UL 9540A propagation behavior belong to the tested pack, not to a pad material.
The mistakes this checklist prevents
| Spec mistake | What it causes | Checklist item that catches it |
|---|---|---|
| Thickness fixed before swell allowance | End-of-life deflection lands in the densification knee; force spikes | Items 2 and 4 together |
| Durometer instead of a CFD window | A foam that measures right on day one but relaxes or sets early | Item 5 plus the data-sheet review |
| Generic preload number from a forum | A window wrong for your chemistry and format | Item 5, taken from the cell supplier |
| No liner plan until launch week | Pads that stretch or misplace on the line; rework | Item 7 |
| Flame class assumed family-wide | UL 94 listings are grade- and thickness-specific | The TDS check in the material direction step |
Frequently asked questions
Can H-O recommend the pressure window for my cells?
No, and a converter that offers to should worry you. The preload window is chemistry- and format-specific and belongs to your cell supplier's guidance, supported by your own validation. What H-O does is downstream of that number: select a family, grade, and thickness whose CFD plateau keeps the force inside your window from beginning-of-life gap through end-of-life swelling, and convert it to your drawing.
What if I only have the BOL gap and a footprint so far?
Send them. That is enough to open the review, narrow the family, and produce first-pass thickness options. Engineering will return a short list of the specific numbers still needed (typically the swell allowance and the pressure window) before a grade is committed, so the quote lands as soon as those arrive.
Do I need separate specs for cell-to-cell and cell-to-module pads?
Yes, treat them as two parts. The cell-to-cell pad is the thin, usually softer layer between adjacent cells; the cell-to-module or end-plate cushion is thicker and usually firmer because it absorbs the accumulated swelling of the whole group against the frame. Both follow the same physics (plateau placement, low set, low relaxation), but the grade and thickness answers usually differ, so the checklist applies once per position.
How are samples and first articles handled?
Samples typically ship in 3 to 5 business days for common die-cut configurations on materials we keep on hand; tooling-free methods (laser, waterjet) cover prototypes so you validate the stack before production dies are cut. First-article inspection is available on request, and standard production after drawing approval runs about two weeks, with special orders quoted to the job.
Send the checklist, get a compression-pad quote
Attach the stack drawing and as many of the eight items as you have. Drawing review typically starts the same business day.
Samples typically 3 to 5 business days; production about two weeks; MOQ varies by material and part. Expedited service available.
Family-owned in Winsted, Connecticut since 1971 · ISO 9001:2015 certified · OEMs worldwide send us a drawing — and get back their part.
Related reading
ApplicationEV Battery Compression & CushioningRead →
GuideChoosing an EV Cell Compression Pad: PORON Microcellular Polyurethane vs. BISCO Silicone FoamRead →
GuideThe CFD Plateau, Compression Set, and Stress Relaxation: Why Compression Pads Hold or Lose Their ForceRead →
IndustryEV & Battery hubRead →
Request a quote for your EV cell compression & cushioning part
Send H-O your drawing or describe the part—engineering reviews every RFQ and converts samples on your geometry.
Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
References
- ASTM D3574 Test C and ISO 3386 (compression force deflection); ASTM D395 and ASTM D3574 (compression set); ASTM D6147 / ISO 3384 (stress relaxation).
- UL 94 (foam flammability classes HBF, HF-1, V-0); UN 38.3 and UL 9540A (pack-level context only).
- SAE Technical Paper 2024-01-2430 and the stack-pressure research record (Cannarella & Arnold 2014; Journal of Power Sources 2021, 2025) behind the pressure-window guidance.
- Manufacturer technical data sheets: PORON industrial 4701/4790 series, PORON EVExtend battery grades, BISCO HT/BF closed-cell silicone foam, V-0 silicone sponge.
This checklist supports a quotation workflow; it does not constitute design guidance for any specific pack. Grade-level properties are confirmed against the manufacturer's current technical data sheet, and pack-level test outcomes belong to the tested pack. All parts are custom manufactured to order; minimum production run quantities vary by material and part. H-O is a die-cut converter, not a raw-material producer, and does not certify cells, modules, or packs.