CERTAINTEED 902018 8'4" x 50' Smart Vapor Retarder Barrier Helps Prevent Mold Better Than Poly Sheeting, Use Unfaced Insulation, Perfect Remodeling Model 902018 is for 8 foot tall walls and is 50 feet long Unlike traditional vapor retarder, membrain helps prevent mold by sensing and adapting permeance to varying humidity throughout the year to keep the wall cavity dry For use with un-faced insulation as a vapor retarder in climate zones where one is required Prevents moisture vapor from entering the wall cavity in the winter and allows any moisture buildup to escape the wall cavity in the summer Installs like poly with an extra level of moisture protection