Kingspan's Thermaroof TR21 (Pack Only) Roofing board is a high performance rigid urethane insulation designed to insulate beneath partially bonded built-up felt and mastic asphalt. It is faced on both sides with glass reinforced perforated cellulose autohesively bonded to the insulation core during manufacture. The core of Kingspan Thermaroof TR21 is a high performance CFC/HCFC free rigid urethane insulant.