J-Drain 5934850JD 400 48" x 50' Dimple Core Drainage Composites. Consists of a moderate-duty impermeable polymeric sheet cuspated under heat and pressure to form a high-flow dimpled drainage core. The core is then bonded to a layer of non-woven 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.