a barrier membrane for use in building construction may be manufactured by forming a polymeric film coating on release paper or film ; or on nonwoven textiles , paper , fiberglass , or other structural substrate to improve tensile strength . alternatively , the film may be fully or partially formed and then bonded to a structural substrate . a porous film coating or laminate may be formed using pvdf , pvc , and various polyolefins . a typical membrane may be less than 100 mil thick and greater than 50 % porous , and may have a hydrostatic head while retaining gas permeability . some embodiments may contain active ingredients to combat bacterial or fungal growth , repel insects , or absorb environmental pathogens . the active ingredients may be applied after the porous film is manufactured or may be incorporated during the film manufacturing process .