Chimney Drains are wide strips of .4" profile dimple drainage core bonded to Caltrans Class B/C filter fabric. Their purpose is to draw the ground water which migrates through the soil adjacent to the wall and quickly convey the water down to the base collection system, providing hydrostatic relief. Often dense compacted soil layers form between the base part and the top of the backfill and water collecting against the wall has difficulty finding its way to the base collection system. Chimneys add very little to the overall cost of the system, but greatly enhance the effectiveness of the drainage system. J-Drain 406 is manufactured using the J-Drain 400 core combined with a Caltrans Class B/C filter fabric.