25 mm prices for 4×8 ft hdpe 500 sheet-HDPE high density. HDPE/HDPP (high-density polyethylene and high-density polypropylene) is also non-toxic and non-staining. Plastic Sheets / Plastic Plywood. Sheet goods me in standard 4′ x 8′ sheets and range in thickness from 1/16″ to 3/4″. In volume quantities, up to 1-1/2”.