Source separation of waste streams and toxic content restrictions are crucial actions toward optimizing the value of recycled feedstocks in building products. HBN’s research on glass waste – known as cullet – reveals the multitude of economic and environmental benefits of these practices. The ability of fiber glass insulation manufacturers to incorporate cullet increases; the wasteful landfilling of discarded glass (nationally, only 28% is recycled) decreases. Manufacturers need less energy to produce insulation, leading to lower greenhouse gas emissions. Workers, surrounding neighborhoods, and the environment at large are exposed to fewer toxic contaminants. Post-Consumer Cullet in California is the second in a series of Healthy Building Network reports for the Optimizing Recycling collaboration.