Polyethylene is the world’s most common plastic. It is used in packaging, food and beverage containers, and consumer products. Building product manufacturers sometimes use post-consumer recycled polyethylene bags and bottles in pipes and plastic lumber. This scrap usually has minimal contents of concern, but products like detergents stored in plastic packaging can remain. So-called “bio-degradation” agents in plastic bags also contaminate this feedstock and should never be used. The plastics recycling industry is developing protocols to screen out residual contaminants. Of greatest concern: Most polyethylene goes unrecycled in the United States due to problems in supply chain controls and the low price of virgin resins. This report examines ways to optimize the use of post-consumer polyethylene in building materials.