Prevents ice buildup on roofs and keeps houses warmer in the winter and cooler in the summer. Made of high-impact polystyrene. Ideal for new construction and retrofit applications. Wide flanges for easy stapling. Full joist coverage for maximum air flow. Installing attic ventilation channels between the rafters or trusses provides an unobstructed air channel through the insulation. Without attic ventilation channels, air cannot flow freely from the soffit to the exhaust vents. Poor air flow reduces insulation efficiencies and accelerates problems due to moisture. 1 ventilation channel per rafter or truss cavity is recommended.