1/4"-4' x 5' POWERHOLD BIRCH 5PLY UNDERLAYMENT | ¼" 4'x5' Powerhold UL6mm plywood premium underlayment is designed for use under vinyl floors, vinyl composition tile, and for general uses where 1/4 inch plywood is an approved floor underlayment. It's unique 5 ply construction gives Powerhold UL6mm floor underlayment a significant advantage over more traditional 3 ply floor underlayments in strength, hardness, and durability. Exterior grade phenolic glue provides added insurance against water damage from floor cleaning and occasional flooding caused by plumbing or appliance failures.