What is the difference between silicone sponge rubber and silicone foam rubber?
Simply put, silicone sponge and silicone foam use different raw materials and different manufacturing processes resulting in slightly different properties
and appearances. Silicone sponge is compounded with a gum type silicone, mixed and processed through a calender, a machine consisting of a series of
hard pressure rollers. Then it is run through a rotocure machine, which continuously vulcanizes the rubber. The characteristic fine fabric
finish on the surface of the silicone sponge is from conveyer belt used in the production process. Silicone sponge is a closed cell structure.
V22-100 is an example of a silicone sponge.
Silicone foam, on the other hand is made from a liquid silicone rubber. These relatively low viscosity liquids can be pumped to the vulcanizing
equipment. The liquid is cast onto a smooth liner (giving silicone foam its smooth surface appearance) and processed through curing ovens.
Silicone foams may be closed cell, open cell or a combination of open and closed cells. V23-000 is an example of a silicone foam.
How do the material properties vary between silicone sponge and silicone foam?
While both silicone sponge and silicone foam have good sealing properties at elevated temperatures, there are subtle differences in the materials.
Silicone sponge is compounded and mixed on a 2 roll mill and then cured in an oven. Silicone foam is made from a liquid silicone which is extruded
and cured in an over. Both are cellular in nature. Silicone sponge tends to be higher in density, have higher tear strength and has a higher use temp
(up to 500F compare to 392F for silicone foam). Basically silicone sponge has higher physical and mechanical properties than silicone foam. Silicone
foam tends to be softer, lower in density and has lower compression set characteristics. Because it contains more air, it provides better thermal
insulation. Silicone foam also has better flame retardant characteristics which are desirable in aerospace applications. Neither material
absorbs much water, so silicone "sponge" is sometimes a confusing description.
What is the difference between silicone sponge per MIL-R-6130, Type 2, Grade A, B and C?
MIL-R-6130 is a military specification for chemically blown, cellular rubber. Type 2 is closed cell. Grade A is oil
and flame resistant, Grade B is non oil resistant and Grade C is Low temperature, non oil resistant. V22-300 is an example of Grade A and
V22-100 is an example of Grade B and C.
