Consists of a impermeable polypropylene sheet cuspated under heat and pressure to form a high flow dimpled drainage core. The core is then bonded to a layer of nonwoven filter fabric. The filter fabric retains soil or sand particles as well as freshly placed concrete or grout, allowing filtered water to pass into the drainage core. J-Drain® 420 Maintains a very high flow rate while providing a higher compressive strength for greater depths. A very popular choice for vertical and horizontal single sided drainage applications. Moderate duty.