Building insulation is used to provide thermal, acoustic, fire, and impact insulation in buildings. It works by reducing heat transfer to help maintain comfortable temperatures. Common places for insulation include walls, attics, basements, floors, and ducts. Insulation saves energy, cuts operating costs, and improves occupant comfort by creating a more uniform temperature environment. The type of insulation used depends on factors like a building's needs and the material's health and environmental impacts.