Celotex insulation boards are made from polyisocyanurate (PIR) foam and have a foil facing on each side. Created by combining polyisocyanurate resin with a blowing agent, it creates a chemical reaction, making the foam insulation. This foam is placed between two emissivity aluminium foil facings and can be cut down to size to suit a variety of building projects including roofs, walls, and underfloor heating.