There are three types of PE, High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE) and Linear Low Density Polyethylene (LLDPE), in more than 70 grades in total.
High density polyethylene (HDPE) is a thermoplastic made from oil. HDPE is resistant to many different solvents and is often used in food containers (certain tupperwares, containers for milk, liquid laundry detergent, etc.), some plastic bags, and containment of certain chemicals, chemical resistant piping systems, and geothermal heat transfer piping systems.
MDPE has good shock and drop resistance properties. It also is less notch sensitive than HDPE, stress cracking resistance is better than HDPE. MDPE is typically used in gas pipes and fittings, sacks, shrink film, packaging film, carrier bags and screw closures.
LDPE has resistant to impact (doesn’t break easily), moisture (water proof), and chemicals (can stand up to many hazardous materials).
LLDPE has higher tensile strength and higher impact and puncture resistance than LDPE. It can be used to make thinner films, with better environmental stress cracking resistance. It has good resistance to chemicals and to ultraviolet radiation. It has good electrical properties. However it is not as easy to process as LDPE, has lower gloss, and narrower range for heat sealing. It is used for plastic bags and sheets (where it allows using lower thickness than comparable LDPE), plastic wrap, toys, lids, pipes, buckets and containers, covering of cables, geomembranes, and mainly for flexible tubing.