Cut and Nail Down a Smooth Plywood Underlayment Arrange the 1/4-in. underlayment on the floor in the approximate shape of the bathroom floor and tape the sheets together with duct tape.

As a builder and flooring installer ... OSB tends to be heavier than plywood. A 4X8 sheet of 3/4-inch sheet of OSB weighs 78 pounds while a comparable sheet of plywood weighs only 67 pounds.