THERMAFLEX M-KE HVAC DUCTS HAVE A VINYL COATED SPRING STEEL WIRE COIL CONSTRUCTION THAT IS IDEAL FOR LOW, MEDIUM PRESSURE HEATING AND COOLING ENVIRONMENTS. THESE HIGHLY EFFICIENT FLEX DUCTS FEATURE A CORE THAT IS BONDED TO THE STEEL WIRE COIL TO SUPPORT THE FIBERGLASS INSULATION. DUCT INSULATION IS AVAILABLE IN THREE DIFFERENT R-VALUES FOR VARIED THICKNESS: R-4.2, R-6.0 AND R-8.0. THE ACOUSTICALLY RATED, POLYETHYLENE INNER LINER ON THESE HVAC DUCTS ELIMINATES NOISE AND EASILY EXPANDS. SPIRAL DUCTS ARE MOLD AND MILDEW RESISTANT. TEMPERATURE RANGE IS FROM -20F TO 200F AND -20F TO 250F INTERMITTENT. INNER CORE IS SELF-EXTINGUISHING. DUCTS MEASURE 4-20″ IN DIAMETER. GREENGUARD CERTIFIED.