This report was prepared by PNNL for DOE's Building America program and is intended as a guide that energy performance contractors can share with homeowners to describe various insulation options for improving the energy performance and comfort of existing homes. The report provides descriptions of many common insulation types, including their advantages and disadvantages, R-values, characteristics, and typical uses. The report also describes potentially hazardous products such as asbestos and formaldehyde and safety issues when conducting energy-efficient upgrades including radon. The guide is available for download at the DOE Building America website, www.buildingamerica.gov.