Silicone Sponge UL 94 HB | Flame Retardant | National Silicone

UL 94 HB Flame Retardant Silicone Sponge

Closed Cell Silicone Sponge

This medium closed cell flame retardant silicone sponge is ideal for sealing and gasket applications where flame resistance and fire safety are a top priority.

Blue Grey Silicone Sponge

This material has received a UL 94 HB and UL94 HF-1 rating for flame resistance and features a blue/grey hue. It The material is produced with a fabric impression on both sides, is flexible and offers excellent compression set resistance.

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



  • UL 94 HB
  • UL 94 HF-1



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



-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 & HF-1 rating UL 94

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National Silicone 30-SIL-SPG-FLR-GRB FR Medium Cellular Silicone_202312
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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.


UL94 HF-1

  • UL94 HF-1 tests measure the ability of a plastic material to resist ignition and burning when exposed to a flame. The test evaluates both the rate at which the material burns and how quickly the flame extinguishes after the source of ignition is removed.
  • Materials rated as UL94 HF-1 are considered to be highly flame-retardant. This means that they are less likely to catch fire and will self-extinguish more rapidly compared to materials with lower flame resistance ratings.
  • UL94 HF-1 rated materials are commonly used in environments where fire safety is a critical concern. These include electrical appliances, electronic equipment, and other products where fire resistance is crucial to ensure safety and compliance with fire safety standards.
  • Achieving a UL94 HF-1 rating indicates that a plastic material meets stringent safety standards for flame resistance. This can be a significant factor in product design and selection for manufacturers who need to comply with fire safety regulations in various industries.



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