Closed cell vs open cell EPDM foam

Same polymer, two completely different behaviours. The cell structure — sealed or interconnected — decides whether the foam stops water and heat, or absorbs sound.

The structural difference

Both grades start from EPDM rubber. In closed cell foam each cell is a sealed pocket of gas: nothing passes between cells, so the material resists water and vapour and insulates thermally. In open cell foam the cell walls have ruptured, so the voids connect to each other and to the surface: air can move through the material, which is exactly what makes it a good acoustic absorber.

Closed cell EPDM foam with sealed cells for water and thermal sealing — Closed cell: sealed cells, low water absorption, thermal insulation.

Open cell EPDM foam with interconnected cells for sound absorption — Open cell: interconnected cells, softer, better sound absorption.

Behaviour side by side

Property	Closed cell EPDM	Open cell EPDM
Water absorption	Very low — sealed cells	Higher — water can enter the cell network
Thermal insulation	Best — trapped gas is the insulator	Lower
Sound absorption	Blocks and reflects	Best — moving air dissipates acoustic energy
Softness / conformability	Firmer, resists compression	Softer, conforms to uneven surfaces
Sealing against water, dust, vapour	Best	Not suitable
Typical density range at Gabrielia	70–200 kg/m³	80±10 / 100±10 / 120±10 kg/m³
Typical thickness range	2–40 mm	2–60 mm
Hardness	Shore 10–20 (customized)	Customized

Choose closed cell when…

The part must stop water, moisture or dust — exterior seals, HVAC lines, refrigeration piping.
Thermal insulation is the main function, or condensation control matters.
The seal needs reliable recovery after being compressed for years.
The application is automotive sealing: doors, windows, glazing, expansion joints.

Choose open cell when…

The goal is sound absorption in vehicles, appliances, machinery or buildings.
The foam must sit against uneven or curved surfaces and stay soft.
Breathability is required, or the part is laminated behind another barrier anyway.
You need thicker sections — our open cell range goes up to 60 mm.

Practical tip. Many acoustic parts are built as a sandwich: an open cell absorber facing the noise source and a closed cell or dense layer behind it for blocking. If you tell us the noise problem and the available space, we can suggest the combination and thickness.

Customization available on both structures

Both open and closed cell grades can be supplied with a skin on one or both faces, in sulfur-free versions for metal contact, and in big-cell, small-cell or higher-hardness variants. Certifications: REACH and RoHS, with IMDS declarations available for automotive programmes.

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Frequently asked questions

Which is better for sound insulation, open cell or closed cell foam?

Open cell foam generally absorbs more sound because its interconnected cells let air move and dissipate acoustic energy. Closed cell foam reflects and blocks more, but is primarily chosen for water and thermal sealing.

Does closed cell foam absorb water?

Closed cell EPDM foam has sealed cells, so water absorption is very low compared with open cell. This is why it is used for exterior seals, HVAC and refrigeration insulation.

Can open cell EPDM foam be used outdoors?

EPDM itself is highly weather resistant, so open cell EPDM foam holds up outdoors better than many open cell materials. However, because water can pass through the cell structure, it is normally used indoors or behind a closed barrier.