Silicone Sponge UL 94 HB | Flame Retardant | National Silicone

Medium Flame Retardant Silicone Sponge

UL 94 HB Closed Cell Silicone Sponge Rubber

This medium density, closed cell flame retardant silicone sponge is a blue/grey color and is rated UL 94 HB. It is ideal for sealing and gasket applications where flame resistance and fire safety are a top priority. The material is produced with a fabric impression on both sides, is flexible and offers excellent compression set resistance.



  • Blue/grey color
  • Flame retardant
  • Excellent for seals and gaskets
  • High compressibility
  • Low compression set
  • UV/Ozone resistant



  • UL 94 HB



Available in – Continuous rolls or cut sheets
Thickness available (in) – 0.0625 to 0.500
Typical roll lengths (ft) – 25 to 100
Typical roll widths (in) – 36
Surface finishing – Fabric impression finish, both sides
Cell structure – Closed cell
Color – Blue/grey, others available



-103°F to +450°F  (-75°C to 232°C)



Compression deflection (25%) psi (kPa) 6-14 (41-96) ASTM D1056
Density < 0.25” thick pcf (kg/m3) 43 (690) max. ASTM D1056
Density ≥ 0.25” thick pcf (kg/m3) 34 (550) max. ASTM D1056
Compression set (22h, 100°C) % 60% max. ASTM D1056
Tensile strength psi (kPa) 125 (862) ASTM D412
Flammability HB rating UL 94

More information found on the full specification sheet. Go To Datasheets




More Information

UL 94 HB

  • UL 94 HB is a is a safety and flammability standard by Underwriters Laboratories.
  • This material is compliant with the UL 94 HB test standard for flammability.
  • The horizontal burn test measures how quickly a horizontally oriented polymer specimen burns across when a flame is applied to one end of the sample.
  • In order for a material to be classified UL 94 HB, it must not have a burning exceeding 40 mm per minute over a 75 mm span for specimens having a thickness of 3.0 mm to 13 mm. For material with thickness less than 3mm the burning rate should not exceed 75mm per minute over a 75mm span. The material will also be rated as HB if it ceases to burn before the 100mm mark independent of thickness.




Request A Quote