Silicone foam board open cell foam and closed cell foam?

The difference between open cell foaming and closed cell foaming?
For foam with open cell structure, due to the interconnection between the cell holes, even if the compression amount used is increased, the path formed between the cell holes can not be completely closed, and can not play a waterproof role. Therefore, in order to achieve the purpose of waterproof, foamed silicone with open cell structure can not be used for shell sealing. Obturators offer certain advantages and disadvantages in applications. The foams can be very light in weight because the pore walls are very thin, and their resistance to liquid penetration may be very good, but the incompressible air inside the pore makes the overall material very hard