For use in replacement siding operations to provide a level surface over old siding, add insulation and weather protection. Kingspan® GreenGuard® P1450 siding underlayment comprises 1/4 in THK closed cell polystyrene (XPS) with perforated cap sheets on both sides. it is configured in fan folded bundles 4 x 50 ft with cut-n-fold hinges. it is lightweight and easy to cut and install. it is designed to be used as a "leveling board", added insulation and added moisture protection in installation of new vinyl siding over old siding. panel rigidity, water resistance, durability, easy cutting and excellent lay flat properties make this product the very best fanfold siding underlayment.