What thickness sponge tape do I need?

Enter the gap you need to seal and we’ll work out the right thickness of EPDM sponge tape, then you can add it straight to your basket.

Your gap

Smallest gap

mm

Largest gap

mm

The gap is the same all the way along

Measure the gap with everything closed. If it changes along the length, untick the box and enter the smallest and largest.

How the calculator works

Sponge tape seals by being squashed between two surfaces, so it needs to be a bit thicker than the gap. Sealing guidance for closed cell sponge commonly suggests squashing it by somewhere between about 25% and 40% of its thickness, and by no more than about 50%, as sponge squashed further may not spring back.

Our own data sheet shows the same pattern. Held at 25% compression for 22 hours at 23 °C, our EPDM sponge has a compression set of 13% to 18%. Held at 50%, it’s 30% to 45%. In plain terms, the harder it’s squashed, the less fully it recovers. It also gets firmer: it takes 20 to 40 kPa of pressure to squash it by 25%, and 50 to 70 kPa to squash it by 50%.

So the calculator aims for about 35%, and accepts anything from 25% to 50%.

In practice, the ideal thickness is about 1.54 times the gap, and anything from 1.33 to 2.0 times the gap should work.

How to measure the gap

Close the door, lid or panel and measure the space the tape needs to fill. If you can’t get a ruler in, press a small ball of modelling clay or reusable putty onto one surface, close it gently, open it again and measure how thin the putty has been squashed. Check a few points along the length, as gaps are often wider at one end or in the middle.

Too thin or too thick?

Too thin and the tape won’t be squashed enough to seal, so draughts, water or rattles can get past. Too thick and the door or lid can be hard to close or may not latch, and the sponge may be squashed so much that it doesn’t recover. If your gap varies a lot, it can be better to use different thicknesses on different sections.

Not sure whether you need EPDM or silicone? Try Which sponge tape should I choose? first.

Our EPDM sponge tape is rated for use from −20 °C to +80 °C. It isn’t suitable for oils, fuels, solvents or aggressive chemicals, submerged conditions, or roofing seams and flashing, and it isn’t certified for electrical, structural, submerged, automotive safety critical or load bearing applications. Full details are in the EPDM data sheet (PDF).

This calculator gives general guidance only. How well a seal works also depends on how firm the sponge is, how much force closes the gap and the surfaces involved, so test a short length before relying on it for anything critical. Questions? Email sales@flashbacktape.co.uk.

Sources

• EPDM Sponge Rubber Sealing Tape data sheet, FB-DS-EPDM Issue 1, Flashback Tape: compression deflection, compression set, thicknesses and operating temperature.
• How much compression do rubber gaskets require?, Elasto Proxy: typical compression ranges for closed cell sponge, including EPDM sponge.
• Gasket compression, Elasto Proxy: ideal and maximum compression, and compression set.
• The mechanics of enclosure seal design, Rogers Corporation: choosing a seal slightly thicker than the gap.