XPS foam core is highly resistant to water absorption but is not technically “waterproof” like a membrane. Its closed-cell structure prevents liquid water from penetrating, with water absorption by volume typically less than 1% when tested per ASTM C272. This exceptional moisture resistance is its defining feature.
Yes, it is the premier choice for below-grade and wet-condition applications. It is extensively used for:
- Foundation and basement wall insulation (placed on the exterior side of the waterproofing membrane).
- Plaza decks and inverted roof systems (where insulation is placed above the waterproofing).
- Perimeter insulation for slab-on-grade floors.
- Cold storage and freezer floors.
Its resistance to freeze-thaw cycles and inability to wick moisture prevents loss of R-value and structural degradation in these demanding environments.
