UL181B-FX tape. Meets LU 181B-FX code for sealing flexible air ducts and air connectors. Conformable and hand tearable.Single-ply construction; will not delaminate upon aging. Used to tape and seal joints and seams of fibrous duct boards,metal ducts, flexible ducting, and insulation facing in ventilation and construction industry. 2.5" x 60 yd.