Silicone sponge, also called closed cell silicone sponge or expanded silicone, is derived from a thin sheet of uncured silicone gum that expands to a controlled thickness while curing in a high temperature press or rotocure operation. Closed cell means that the cells are non-interconnecting, therefore they do not allow water to wick through the sponge. Generally, silicone sponges have superior mechanical properties and are considered to have a complete closed cell structure. Silicone sponge often provides better water sealing in wash-down applications as compared to silicone foam.

Silicone foam is normally considered to be an open cell, lightweight product that is derived from liquid silicone ingredients that are cast onto a liner and cured in an oven. Higher density silicone foams have been developed, in recent years, that are suitable for water sealing. Low density open cell silicone foams may allow moisture to pass through the cell structure unless the design allows for extensive deflection of the gasket. In contrast, higher density silicone foam products will have a higher proportion of closed cells compared with medium or low density grades. With the proper amount of deflection, it is possible to achieve a good long term weather seal and rain seal with silicone foam.