Very frequently used cheap plastic out of the family of polyolefins with a linear structure of polymers. For most applcations it is used without additives and modifications. This favors a lot recycling and makes it harmless for humans and enviroment. Therefore it is a prefered material for packaging including food packaging. It is flamable and it burns with high energetic efficiency (like gasoline).
Despite its simple structure several groups with significantly differing properties exist. The main differentiation is based on the difference of molecular mass. Generally PE is formed by extremely long polymers from 300.000 g/mol (LLDPE=Linear Low density PE) up to many million g/mol (UHMWPE = Ultra High Moelcular Weight PE). While LLDPE is a very easily processable mass material which mainly is used for extrusion, the melt of UHMWPE practically is no more fluid because of the large molecules and extrusion and injection moulding is no more possible. The only possiblity of processing is sintering what causes high costs to create finished products. It has its main applications because of its superior abrasion resistance.
The tear strength of polyethylene is not very high by virtue but can be extremely increased by stretching. This not only causes orientation of molecules in stretch direction but also an elongation of molecules. This increases strength in tear direction a lot. By this process textile fibres of extreme strength can be produced (Dyneema, Spectra)