The company's MemBrain™ vapor retarder is a polyamide film that changes permeability from less than 1 perm at low humidity to greater than 20 perms at high relative humidity. With a high resistance to water vapor diffusion in the winter, MemBrain reacts to rh increases by altering pore size, allowing water vapor to pass through it. The lowered resistance supports the drying process, according to the manufacturer.