If your air conditioning unit is on the fritz or you're in the process of building a more...

It's used as foam insulation, upholstery stuffing, shiny wood-floor sealant, and more. This synthetic polymer is strong, lightweight, and versatile. It is highly effective as an insulator, which earns it green points, though it is obviously not eco-friendly from a resource standpoint, since it's petroleum-based. Polyurethane foam insulation was traditionally blown in with CFCs or HCFCs, which are known ozone depleters. Today, more eco-friendly blowing agents are used with this material, and it's a component of structural insulated panels (SIPs), a construction element that is generally smiled upon by green builders.

Many homeowners know very little about their heating and cooling equipment-until something goes...