Polystyrene Foam Rafter Vents assist in the constant flow of fresh air from soffit vent to the ridge by creating an airway from the soffit to the ridge. A balanced ventilation system to helps provide comfort in all seasons and helps to prevent roof damage due to moisture trapped between the insulation and roof sheathing. - Polystyrene Foam Rafter Vent, 24 in. x 40 in.