Solid base shells are manufactured without cavities and fillers; they are stronger than hollow bases, and there are no traps for bacteria and fungi to grow. In the thermoplastic shell, the sturdy base will not break under steam or high-pressure washing. The hollow base saves material and weight to reduce costs. Some people use epoxy resin to backfill the hollow base to eliminate the trap of bacteria breeding, but this will not increase the strength, will cause the installation surface to be uneven, and water will seep between the shell and the filling material, causing cracking.