ATCO #030, #036, and #031 are UL 181, Class 1 Air Ducts and are manufactured with a tri-directional fiberglass scrim reinforced, metallized polyester outer jacket. A double lamination of tough polyester which encapsulates a steel wire helix forms the air-tight inner core of the ATCO #030, #036, and #031. The double-layer core of each product is wrapped with a thick blanket of fiberglass insulation. The inner core of all three products is air tight and designed for low-to-medium operating pressures in HVAC systems. ATCO #036 and #031 have increased insulation for superior thermal performance.