Water or moisture may increase
the thermal conductivity of some insulants. This is critical
in some applications such as perimeter or roofs.
Rigid polyurethane insulation is hardly affected by water
or moisture:
insulation
materials made of rigid polyurethane foam do not absorb
moisture from the air. Due to their closed cell structure,
they do not absorb or transport water, i.e. there is
no capillary action. For this reason, normal moisture
in buildings does not lead to an increase in thermal
conductivity. Water vapour diffusion cannot cause increased
moisture levels in rigid polyurethane foam insulation
boards unless these have not been properly installed
from a structural point of view, for example where vapour
barriers are lacking, or due to air pockets or faulty
seals.
Water absorption of rigid polyurethane foam
after 28-day immersion in water
