Lightweight Polystyrene Knee Boards measure 30 In. x 10 In. and are made from tough, heavy-duty polystyrene plastic. These concrete sliders have rounded edges to prevent digging into concrete. The polystyrene prevents corrosion and allows easy use of boards with plastic that is easy to clean. The white material is non-marking. Toe bracket secures the foot and allows for ease of back and forth movement along the work surface. Each board has an adjustable knee pad to provide comfort on your knees as you move around the cement. Knee pads are made of durable, lightweight polyurethane with two adjustable web straps to hold pads to knees. Each pad is molded in one piece to eliminate seams that can lead to chafing and discomfort. Remove the knee pads and use them on their own for additional versatility. The knee pads are replaceable to extend the life of the sliders.