12mm HDPE sheets for HDPEpbuilding HDPE Plastic Sheet (5 Sheets) 12" x 24" x 1/4" - Black Marine 5 Pack 12 x 12 x.125 Black HDPE Sheets, Great for DIY Projects for Home and Marine Applications, Black Plastic Sheets, High Density Polyethylene Sheets, Made in USA $22.95 ($4.59/Item) In Stock. Get Price. Get Price.