A vapor pressure–distributing / partially adhesive underlayer is mainly needed in a two-layer bituminous welded system to prevent blistering in the waterproofing caused by any trapped moisture.
IKO Enertherm is a PIR insulation with a closed-cell structure and a vapor-tight facing. This means that any moisture trapped between the insulation and the bitumen layer cannot easily escape.
With rising temperatures, this moisture can expand and cause blistering. The vapor pressure–distributing underlayer ensures that any vapor pressure is dispersed and released without damaging the roofing membrane.
Furthermore, partial adhesion on the faced IKO Enertherm insulation guarantees good bonding results for wind stability.