Roberts First Step Premium 3-in-1 Underlayment is ideal for use under laminate and hardwood floating floors. It can be used over concrete and wood subfloors, and because of its sound resistant qualities, it reduces ambient noise, making it great for use in condos and multi-level dwellings. This premium underlayment features Air Flow Technology to minimize the damage cause by trapped moisture, a 3-layer design with polystyrene beads to allow moisture to flow to the exterior walls to be released safely, and a 2-mil top layer that protects the finished floor from subfloor moisture. It offers outstanding compression resistance and mold / mildew defense. For residential and commercial use, it can be installed below, on, and above grade. This 100 sq. ft. roll measures 40 in. x 30 ft.