The Lambro FMD-425 is a premium 4-inch diameter by 25-foot long insulated flexible air duct engineered for standard residential and light commercial HVAC air distribution systems. This flexible ducting line is ideal for connecting bathroom exhaust fans, kitchen range hoods, inline ventilation systems, or fresh air intakes to main metal trunks or exterior wall termination caps.
This high-performance ducting features an R4.2 thermal resistance rating supplied by a thick fiberglass insulation blanket wrapped around a flexible core. This thermal layer prevents condensation build-up caused by temperature differentials while minimizing radiant heat loss or gain. The exterior is wrapped in a tough aluminized polyester vapor barrier jacket that resists tears and punctures during tight runs.
Complies with industry standards including c-UL-us Air Duct requirements and NFPA 90A & 90B regulations, making it a safe choice for building inspectors and professional installers. Mechanical contractors select the FMD-425 because its flexible design speeds up routing through joists, while the Greenguard Gold certification ensures the product supports healthy indoor air quality.
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