Aquabar® "B" Solid Hardwood Flooring Moisture Vapor Retarder *****SOLD BY THE ROLL (500 sq ft. per roll) In the battle against interior moisture damage, the best defense is a strong offense. When you block moisture vapor from creeping underneath finish materials or reaching moisture sensitive substrates, you help increase the useful life and appearance of finish surfaces. To help win the battle, the Fortifiber Building Systems Group offers Aquabar "B" as inexpensive insurance to reduce moisture-related problems. Aquabar "B" floor and tile underlayment is an extremely effective moisture vapor retarder for use in a variety of interior construction applications. Consisting of two layers of kraft paper laminated with asphalt, Aquabar "B" is a non-reinforced 30/30/30 duplex type Grade "B" paper.