Flexmaster U.S.A.® HVAC Product Line - The Best Air Distribution Products in the Industry. Flexmaster U.S.A.®, located in Houston, TX, is a leading commercial HVAC flexible duct and sheet-metal fitting manufacturer with over 35 years of success in the industry. Our renowned Flexmaster U.S.A.® HVAC product line of Air Distribution Solutions includes: flexible ducts, acoustical ducts, sheet-metal fittings, access doors, low leakage access doors and accessories for both commercial and residential applications. Flexmaster U.S.A.® is a registered product line of Masterduct, Inc. www.Masterduct.com www.FlexmasterUSA.com