There are three categories of roof insulation: rigid board, non-rigid (batt, blanket, or loose fiber) and sprayed polyurethane foam. Rigid boards are typically used in low-slope assemblies. They may be polyisocyanurate (most common), extruded polystyrene, or mineral wool. Non-rigid insulations are typically used in attic spaces and in pre-engineered buildings. See the section on Sprayed Polyurethane Foam for more information on this type.