T.R.U. AF-20R Heat Shield Resistant Aluminum Foil Tape: 3 in. wide x 50 yds. (2Mil) 3.6 Mil Aluminum Foil: 1.6 mils (adhesive) + 2 mils (carrier) - 3 in. Core Resist water vapor, some chemicals, flame, moisture, weather and smoke transmission. Acts as a vapor barrier to insure the integrity of the insulation system Thermal conductivity helps cooling and heating efficiency, improving efficiency in systems Conformable backing and pressure sensitive rubber adhesive adheres to a variety of smooth or irregular surfaces