Polyethylene sheet is a very strong plastic that can be found in items ranging from shopping bags to bulletproof vests. Thin sheets of polyethylene are sold in rolls and used in many commercial and industrial activities. The material does not rot, and it is resistant to many chemicals. It is not damaged by extreme weather, which makes it a good choice for many kinds of outdoor applications, and the sheets can be reused many times. Polyethylene is used for many kinds of weatherproofing and can be a permanent weather barrier on exterior walls.