Although the thermal conductivity of an average silicone elastomer is quite low at around 0.2 watts per meter, the elastomer can only be used as an efficient thermal insulation material in porous form. The gas in the many pores significantly increases the thermal insulation effect. However, it is essential that the material’s pores are neither interlinked nor connected to the ambient air – every individual pore is isolated. Experts refer to this kind of pore structure as closed-cell.
If the pores were open, convection would enable the gas to transport heat from the hot to the cold side. Dr. Storre generates the closed-cell pore structure in his insulation material with the aid of tiny, extensible, hollow spheres that are filled with a gas. “Mixed into the silicone rubber, these hollow microspheres represent gas-filled pores. In every individual microsphere, the gas is trapped like in a balloon,” explains ContiTech’s elastomers expert.
Furthermore, ContiTech treats the material with a heat stabilizer and a flame-retardant additive. As a result, the microporous elastomer achieves a thermal conductivity of only 0.08 watts per meter and Kelvin, measured at 200 degrees Celsius. “This brings our silicone insulation material to the same level as mineral wool. A ten-millimeter-thick insulation layer is sufficient to reduce heat losses by around 65 percent,” emphasizes Dr. Storre.