Firestone EPDM Liner & Underlayment Kit, 15'x20', 45 mil Contains 15' x 20' Firestone EPDM Pond Liner, 45 mil Included 15' x 20' section of Premium Geotextile Pond Underlayment Liner shows outstanding resistance to ultraviolet radiation (UV), ozone and other environmental conditions Liner is tested for the safety of fish and aquatic plants. Underlayment is a nonwoven, synthetic fabric that protects the liner from punctures.