Short answer: XPE foam does not absorb water. Every cell is closed and sealed, and measured water absorption is 0.4% or lower. But "the foam does not absorb water" and "an assembly built from it is waterproof" are two different claims, and it is worth keeping them apart.
Why Closed-Cell Foam Does Not Absorb Water
In an open-cell foam the cells are interconnected, so water wicks into the material through the cell walls and stays there — the foam gets heavier, loses insulation value and becomes a place for mould to grow. In a closed-cell foam each cell is a sealed pocket. There is no path for water to travel through the material, so the foam can only take on the small amount of moisture that clings to its cut edges and surface.
Measured Water Absorption
| Material | Water absorption | Notes |
|---|---|---|
| XPE | 0.4% or lower | Falls as density rises: 0.2% at the higher densities |
| IXPE | 0.4% or lower | Also specified as resistant to seawater, oils, acids and alkalis |
For context, an open-cell polyurethane foam can take up many times its own weight in water. A figure below half a percent is what makes a closed-cell foam usable in a wet environment.
Water-Resistant Is Not the Same as Waterproof
The foam is water-resistant: it will not soak up water, rot, or lose its buoyancy and insulation value. It is not, by itself, a waterproofing membrane. Water can still travel past a sheet of foam at a cut edge, a joint, a seam or a fixing point, and it can travel along the interface between the foam and the surface it is bonded to.
Where a project needs a genuine barrier, the foam is part of an assembly: a foil or film facing provides the vapour barrier, and the joints, overlaps and penetrations are sealed. That is how a foil-faced, self-adhesive pipe wrap works, and it is why the facing and the adhesive matter as much as the foam.
Chemical and Seawater Resistance
Beyond fresh water, our factory data specifies IXPE as resistant to seawater, oils, acids and alkalis, and describes it as antibacterial, non-toxic and odourless. That combination is why closed-cell polyethylene foam is used for marine flotation, outdoor cushions and wet-area products.
Where XPE Foam Works in Wet Environments
- Pipe and duct insulation — the sealed cell structure is what prevents condensation from being absorbed into the insulation.
- Marine and flotation — the foam does not take on water, so buoyancy stays stable in service.
- Outdoor furniture and camping mats — rain and ground moisture do not soak in, and the foam can be wiped dry.
- Wet-area flooring underlayment — closed-cell foam does not wick moisture the way an open-cell underlay does.
When You Need a Waterproof Assembly
If the requirement is a vapour barrier or a waterproof layer rather than a water-resistant cushion, specify the facing and the jointing as well as the foam. Aluminium foil lamination, film lamination, a sealed self-adhesive overlap and closed joints at penetrations are what turn a water-resistant material into a waterproof build-up. Tell us the environment and we will confirm which combination we can supply.
Ask us about foam for a wet environment →
Is XPE Foam Waterproof? FAQ
Does XPE foam soak up water?
No. XPE is a closed-cell foam and its measured water absorption is 0.4% or lower to GB/T 1034. Water cannot travel through the material because every cell is sealed.
Can XPE foam be used outdoors?
Yes. Closed-cell foam does not absorb water, does not rot and does not support mould growth. IXPE is additionally specified as resistant to seawater, oils, acids and alkalis, which suits marine and outdoor products.
Is XPE foam the same as a waterproof membrane?
No. The foam is water-resistant, but it is not a barrier membrane on its own — water can still pass at cut edges, joints and fixings. A waterproof build-up uses a foil or film facing with sealed joints, with the foam providing the cushioning and insulation.
Related Reading
See also: Flotation foam: density and buoyancy · Marine & outdoor foam · All cross-linked foam materials · Contact Bofeng Foam