Why does Regupol® / Regufoam® have to be covered with PE foil before applying concrete?

Regupol® / Regufoam® for vibration insulation or impact sound insulation under screed is covered with commercially available PE foil (0.2 mm) to avoid any structure-borne noise bridges from forming as webs. Given Regupol®'s open fibre structure, in-situ concrete could settle in the material and cause the resilient bedding to become stiff; in the worst case, this could lead to direct transmission of structure-borne sound. Applying the PE foil also helps to avoid webs forming between the material joints.