Flex duct is a flexible, insulated ductwork made from a helical wire core wrapped with plastic film and covered with fiberglass insulation. This corrugated tubing provides convenient installation in tight spaces where rigid metal ductwork cannot fit. Flex duct typically ranges from 4 to 16 inches in diameter and comes with R-4.2 to R-8 insulation ratings.
Advantages and Limitations
Flex duct simplifies installation in residential applications and reduces labor costs compared to metal ductwork. However, it is more prone to air leakage than rigid ducts, with studies showing 15 to 30 percent efficiency losses when improperly sealed. It is not recommended for high-temperature applications or areas exposed to rodent damage.
Installation Best Practices
Proper installation requires full support every 4 feet using rated hangers and minimal bends to reduce airflow resistance. All connections must be sealed with UL-181 rated mastic and fiberglass mesh tape. Flex duct should never be compressed or kinked, as this significantly reduces system efficiency and airflow capacity.