Rubber on top, foam underneath, bonded by an adhesive-infused middle layer so the two do not separate when a barbell rack or treadmill parks on them for months. Eighteen 24-inch squares at 0.4 inch thick snap together into 70 square feet of gym floor, and 36 detachable borders square off the edges. The rubber face grips shoes and shrugs off dropped plates, while the high-density foam beneath absorbs impact and cuts the noise that travels into rooms below. Scissors trim the outer tiles for a wall-to-wall fit around door frames and posts. The set works over tile, marble, wood or carpet and weighs 30.5 pounds, heavy enough to stay put once laid and light enough to relocate one tile at a time.