Thickness 5 to 20mm high-impact strength rigid polyethylene . Thickness 5 to 20mm high-impact strength rigid polyethylene sheet for sale HDPE SHEET NATURAL HIGH DENSITY POLYETHYLENE – 12x12x0.250 Quantity: Price per Sheet: $22.16. Total Price: $22.16. Clearance pricing on .25 x 12 x 96 in., .25 x 15 x 15 in., and .25 x 27 x