Polyethylene Sheet HDPE 10mm-12mm-15mm-20mm-25mm-30mm thick High Density Polyethylene Sheet: 10mm to 30mm thick. On this page you can buy High Density Polyethylene, also referred to as HDPE or PE300, in full sheets and custom cut pieces in 10mm, 12mm, 15mm, 20mm, 25mm and 30mm thick.