Different kinds of PE

HIGH-DENSITY POLYETHYLENE (HDPE)

Bags are often made of high density polyethylene (HDPE). This plastic is usually milky white or semi-translucent, has superior puncture, low permeability and temperature resistance, and is more rigid and stronger than LDPE / LLDPE but also tears easier and has a propensity to crinkle. Most shopping, grocery and trash bags in the USA are made of this plastic. HDPE is often chosen for its high strength and low cost.

MEDIUM-DENSITY POLYETHYLENE  (MDPE)

Medium-density polyethylene is less opaque than HDPE but not as clear as LDPE. Bags made of this plastic are usually stronger than LDPE but do not stretch as much. This type of polyethylene is used on a much smaller scale than HDPE and is often used for garbage bags and for consumer packaging.  

LOW-DENSITY POLYETHYLENE (LDPE)

Low density polyethylene or LDPE is another very popular polyolefin. Bags made from this material are either white in color or clear. LDPE is often chosen for consumer packaging where strength is not a requirement like bags for bread, newspapers, frozen food, fresh produce, dry cleaning garments, etc. Bags made from this material are very flexible and easy to stretch, and are clear and glossy. They also have good tear resistance and good moisture barrier properties but only fair gas barrier properties.

LINEAR LOW-DENSITY POLYETHYLENE (LLDPE)

Linear low-density polyethylene has similar properties as LDPE and finds uses for similar applications. However, there are some differences which makes LLDPE preferable for different applications. For example, LLDPE is selected for its higher tensile and impact strength and better heat sealability, whereas LDPE is often selected for its higher clarity, ease of processing and higher gloss. Important applications include shopping, frozen food, garbage, news paper, and general food bags.