Waves or buckles in a fanfold underlayment will be magnified when the siding goes up. Amoco Foam Products Company has introduced Amocor P38/FP38, a 3/8-in. residing underlayment that the company says offers the benefits of a thick fanfolded extruded polystyrene underlayment that lays flat as a board over old siding. The difference, says the company, is in the redesigned hinge that connects the fanfolded boards. The hinge is cut through the entire board, with the individual boards held together in the fanfold bundle by a tough plastic coating. The new hinge creates a seamless product that lays flat. This lets you achieve a solid, level base for new siding.

The product is available with or without a reflective surface. According to the manufacturer, its fanfold design provides consistent, dependable coverage over old siding, eliminating cracks and crevices that lead to energy-robbing drafts. It's sold in bundles of 4-ft. by 50-ft. that are installed over old siding to provide a continuous layer of protection.

Contact: Tenneco (formerly Amoco Foam Products)