It is important when choosing any form of silicone sponge to understand the difference between open and closed cell. Confusing the two could lead to failure of a seal or gasket in application.
Open Cell Sponge
Open cell basically means that each cell, or if you like bubble, is openly connected to the next cell. These cells are not complete closures therefore water, moisture and dust can very readily make their way into the cell structure.
A good example of an open cell sponge