Resistance to moisture

The moisture resistance of the core layer material can have a significant impact on the durability of the external structure of a composite panel, and can affect long term insulation performance.

Moisture in core insulation materials has a negative effect on thermal insulation properties and can contribute to the development of mold. Additionally, trapped moisture conducts heat 25 times better than air. In structures where gas-tight outer layers are not used, moisture can penetrate the core layer material by diffusion and condense. Damage to outer layers can also lead to moisture accumulating in insulation material.

As well as good thermal performance, STYROFOAM™ also provides high water resistance, ensuring a consistently good thermal performance.

Thermal insulation materials are measured according to EN 12088 (water pick-up by immersion) to determine the water resistance. The samples are stored in a water bath for 28 days before measuring the water content (figure 07).


Figure 07: Resistance to water according to EN 12087

The below chart shows water pick-up values for STYROFOAM™, EPS (15kg/m3) and PU, as known from publications. Besides water pick-up values the graph shows the change in thermal performance of materials due to water pick-up. STYROFOAM™ with its closed cell structure picks up very little amount of water. As a result of that the thermal conductivity of STYROFOAM™ doesn’t change significantly after the water pick-up by immersion test compared to the thermal conductivity measured after storage under dry conditions.

Cell structure of XPS Cell structure of EPS Cell structure of PU

Figure 08