Is Isolon or Warmlex waterproof, and does the foam float or sink in water?

Short answer: Isolon and Warmlex are closed-cell PE foams that do not absorb water like a sponge and normally float in water due to their low density. However, this does not turn standard insulation grades into certified marine or lifesaving products.

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This article explains how Isolon and Warmlex behave in contact with water: whether they float, absorb moisture or degrade over time. It is a typical “what if” question from customers using foams in outdoor, DIY or temporary applications.

Closed-cell structure and water behaviour

Isolon 300/500 (IXPE) and Warmlex (non-crosslinked EPE) are closed-cell foams. This means that:

• each cell is sealed and does not communicate with neighbouring cells;
• foam does not absorb water into its internal structure like open-cell sponge;
• water can only remain on the surface or in small gaps between sheets.

Because the density of these foams is significantly lower than that of water, standard grades of Isolon and Warmlex normally float when placed on the surface of water.

Limitations and practical use

From a practical point of view:

• foams can be used where occasional contact with water or high humidity is expected;
• they are often used as a component in camping, leisure and sports products;
• edges and perforations can allow water to enter gaps between layers or under coverings;
• long-term immersion or dirty water may affect appearance and hygiene.

For EU projects, any formal use in aquatic or safety-related environments must follow the relevant standards and test procedures, which go far beyond general material properties.

Drying and re-use after contact with water

— after accidental wetting, wipe the surface and allow the foam to dry in a ventilated area;
— do not dry directly on heaters or open flames;
— check that no dirt, sand or chemical contaminants remain on the surface;
— if used in hygienically sensitive areas (for example, sports mats), the final decision on re-use should be made by the product owner.

Frequently asked questions

• Can I use the foam as a swimming aid? No. Even if the foam floats, we do not supply or certify materials as lifesaving equipment.
• Will the foam degrade if it gets wet occasionally? Occasional wetting is not critical. More important is UV exposure, heat and mechanical damage.