High Impact & Waterproof Plastic Material Medium density polyethylene is used which gives high impact strength at low temperatures yet is very tough and resilient at ambient temperatures, the black color is thoroughly mixed with the base opaque plastic using temperature and pressure prior to the molding process and gives very high resistance to UV (sunlight) degradation and discoloration. There are some case makers who use a dry blending method to add colors to the base opaque plastics, this does reduce costs but gives lower impact strengths and poor color distribution. The polyethylene used by HARDCASE will not absorb moisture and it is resistant to most common chemicals and oils.