Air-Bloc® 21 is a trowel consistency, solvent-type, synthetic rubber-based insulation adhesive formulated for easy application on a range of construction surfaces. Air-Bloc® 21 is designed to provide an effective air and vapor barrier when used as a full bed adhesive in conjunction with rigid foam or semi-rigid paper-faced insulation. Air-Bloc® 21FR is used as a full bed adhesive in conjunction with rigid foam or semi-rigid paper-faced insulation.