Fluorosilicone Rubber Becomes Mandatory Material for Aerospace Fuel System Seals


      The aerospace industry’s transition to higher-temperature, higher-pressure engine designs is driving unprecedented demand for fluorosilicone rubber.
     Commercial aviation and defense contractors are placing increased emphasis on elastomers capable of surviving continuous exposure to jet fuel, hydraulic fluids, and extreme temperature swings ranging from -55°C to 205°C. Fluorosilicone rubber, which combines the fuel resistance of fluorocarbon elastomers with the low-temperature flexibility of silicone rubber, has become the material of record for critical sealing applications.
      Standard fluorocarbon elastomers, while highly resistant to jet fuel, become brittle and lose sealing force below -25°C. This limitation is unacceptable for aircraft that routinely operate at high altitudes where ambient temperatures drop below -50°C. Fluorosilicone rubber, in contrast, retains its elasticity down to -65°C, with a glass transition temperature of approximately -68°C. This low-temperature performance is achieved through the incorporation of trifluoropropyl groups along a siloxane backbone, a structure that resists crystallization even under extreme cold.
       Fuel swell behavior distinguishes fluorosilicone rubber from conventional silicones. When immersed in Jet A or Jet A-1 fuel, fluorosilicone rubber exhibits controlled volume swell of 10-25%, which actually enhances sealing force by compressing the elastomer against gland walls. This compares favorably to standard silicone rubber, which can swell by 50-100% in fuel and rapidly extrude through seal gaps. Conversely, resistance to engine oils and hydraulic fluids containing amine-based additives has been validated through 5,000-hour immersion tests showing no loss of tensile strength or elongation.
       Recent certification data released by materials testing laboratories indicates that new peroxide-cured fluorosilicone rubber compounds achieve compression set values below 25% after 70 hours at 175°C. Compression set, the permanent deformation remaining after a seal is compressed, is the single most important predictor of long-term sealing performance. Values below 30% are considered excellent for high-temperature fuel system applications.
      Aircraft manufacturers are now specifying fluorosilicone rubber for fuel tank access panel seals, quick-disconnect couplings, valve stem seals, and O-rings for fuel pumps. The material’s low outgassing properties in vacuum environments also make it suitable for fuel systems in upper-stage rockets and satellites. With the global commercial aircraft fleet expected to double by 2040, demand for fluorosilicone rubber in original equipment and aftermarket seal kits is projected to grow at a compound annual rate of 7-9%.