A variety of techniques and materials used to retain heat or cold and improve energy efficiency. Placed between wall studs or over floor joists, batt and blanket insulation is made of fiberglass, cellulose, wool, and green or recycled materials such as reclaimed blue jeans. Board insulation is rigid foam attached to walls or wood members with connectors. Sprayed/blown insulation features foam, wool, or cellulose fiber that is sprayed between walls, onto ceilings or foundation walls, or into cavities between floor and ceiling joists.