Technical Data Construction Materials Duct liner is permanently bonded to a corrosion resistant spring steel wire helix, also supporting a blanket of fiberglass insulation. Vapor barrier is an outer jacket of fiberglass reinforced metalized film laminate. Codes / Standards UL 181 / Class 1 Air Duct Operating Pressure (inches water column) Positive = 10 inches H²O (2.5 kPa) intermittent Positive = 6 inches H²O (1.5 kPa) continuous Negative = 1/2 inches H²O (0.5 kPa) Operating Temperature Range @ 6 inches H²O (1.5 kPa) Positive Minimum = -20°F (-28°C) Maximum = 140°F (60°C) @ 2 inches H²O (0.5 kPa) Positive Minimum = -20°F (-28°C) Maximum = 180°F (82°C) @ 1/2 inches H²O (0.13 kPa) Positive Maximum = 250°F (121°C) intermittent Velocity (feet per minute) 4,000 f.p.m. (20 m/sec) R-Value R-4.2 Surface Burning Characteristics Maximum Flame Spread = 25 Maximum Smoke Development = 50 Vapor Barrier Permeance 0.04 perm (2.3 ng / s.m².Pa) Available Diameters 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18 inches Available Lengths 25 feet