Loft insulation. Building insulation refers to materials used to reduce heat loss. The loft or attic space in a house is frequently left unheated, and so insulation is needed at this point to reduce heat loss from the heated area below. Insulation materials range from foam to wood to cork to the fibrous insulation being used here. Fibrous materials used as building insulation include mineral and natural wools and cottons. Behind the insulation are the wooden rafters and joists of the building's roof.