HDPE
High-density polyethylene. Roughly twice the tensile strength of LDPE per micron and much weaker against puncture.
Also called: high-density polyethylene
Right for paper and dry packaging, where a 12 µm HDPE sack does the work of a 25 µm LDPE one using half the polyethylene. Wrong for anything with a corner in it.
It rustles, which is how you identify it by ear.