What is the difference between LDPE and HDPE?

The difference between LDPE and HDPE is simply the density of the material.
 LDPE is manufactured with less tensile strength and therefore a lower-density providing users greater flexibility & more ability to stretch.

HDPE is a very similar material as  LDPE, polyethylene. Just with a few different properties.

LDPE has a softer feel to the end product and has more flexibility.
It also melts at a lower temperature.

Whereas HDPE is slightly harder and has more tensile strength and therefore has a higher-density. Thus making it a stronger bag.

This is useful for applications that require more durability and weight resistance.

While both materials stem from polyethylene and produce different characteristics, they are essentially the same in the most important aspects.

Both are very versatile & extremely useful polymers!