Abstract: A baffle for use in an attic is installed between adjacent roof rafters to substantially block the flow of ventilating air through an opening located between the top surface of the wall plate and the underside of the roof deck. The baffle is formed from extruded cellular plastics material which is cut to define two parallel grooves by cutting through the first wall to define first and second side flaps hingedly connected to the rectangular panel by bending said sheet at said grooves for attaching the side flaps to the inner face of said roof rafters. The first and second grooves are formed in the sheet at right angles to the webs so that the grooves cut through the first sheet also cut at least partly through the webs.