An apparatus for forming venting channels in a continuously-formed foam product includes a plurality of channel-forming plates which are removably attachable to the upper endless-type conveyor of a rigid foam laminating apparatus. The channel-forming plates provide a molding surface to form transverse channels in the foam product during the foaming operation. The channel-forming plates are easily removed for repair and/or replacement and include a centering bar which accurately positions each plate on the endless conveyor. The channel-forming plates are configured to form generally U-shaped channels in the upper surface of the continuously formed foam product to provide venting channels when the foam product is cut and used in roof insulation. The product and venting channels therein are sized to provide a continuous channel when a plurality of the foam panels are used as well as to facilitate attachment to standard trusses or joists.