Firestone 45mil EPDM Rubber Pond Liner 15ft.x15ft. EPDM rubber pre cut and boxed pond liner Pond liners retains its high flexibility even in cold weather It is safe for fish and aquatic plants The black color also lends greater U.V. protection while giving the illusion of greater depth Measures 15-feet width by 15-feet lengthUnit of measure "mil": 1 mil= 1/100th of a millimeter