Water Brick Hot Tub Booster SeatWater Brick Hot Tub Booster Seat The Water Brick Hot Tub Booster Seat is designed to give you a boost in that hot tub seat that is a little to deep. The Water Brick Booster Seat is cushioned for maximum comfort and designed to be filled with washed pea gravel or marbles to ensure that it does not float to the surface. Made of high quality materials and fabrics for years of enjoyment. Booster Seat Features: Gives you an extra boost in deeper hot tub