The most mmon size in the thickness rating for plastic sheeting is 6 mil. This is 6-thousandths of an inch, or 0.006 inch. large hdpe plastic sheets 20mm st-HDPE 4×8 polyethylene . HDPE. Density. 0.96-1 g/cm3. Shore Hardness. 55-70 A. We offer quality assured range of HDPE sheets, also known as High Density Polyethylene Sheets.