BISCO® RS-820 Firm
BISCO® RS-820 is a firm cellular silicone sponge with a density of 25 lb/ft³ and a compression force deflection of 12–20 psi per ASTM D1056, designed to retain the lightness of a foam while providing the enhanced sealing capability of a traditional sponge rubber. The material has a temperature range of -67°F to 392°F, passes UL 94 V-0 and UL 94 HF-1 at a third-party laboratory, and is UV and ozone resistant. RS-820 is an alternative to HT-820.
Key Properties
- Compression Force Deflection: 22.5 psi (ASTM D1056)
- Compression Set, 22 Hours @ 212°F @ 50%: 4.0% (ASTM D1056)
- Water Absorption: 1.0% (ASTM D1056)
- Density: 30 lb/ft³
- Temperature Range: -67°F to 392°F
- UL 94 V-0 / UL 94 HF-1: Pass (Meets at third party lab)
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- Specifications
- Applications
- General Info
- FAQs
Physical Properties
| Property | Value | Test Method |
| Thickness | 1/8″, 3/16″, 1/4″ | — |
| Color | Gray | — |
| Material/Substrate | Silicone Sponge | — |
| Density | 25 lb/ft³ | — |
Mechanical Properties
| Property | Value | Test Method |
| Compression Force Deflection | 12–20 psi | ASTM D1056 |
| Compression Set, 22 Hours @ 212°F @ 50% | 4.0% | ASTM D1056 |
| Water Absorption | 1.0% | ASTM D1056 |
| Low Temperature Brittleness | -67°F | ASTM D746 |
Thermal Properties
| Property | Value | Test Method |
| Temperature Range | -67°F to 392°F | — |
Flame & Fire Performance
| Property | Value | Test Method |
| UL 94 V-0 | Pass | Meets at third party lab |
| UL 94 HF-1 | Pass | Meets at third party lab |
Environmental Performance
| Property | Value | Test Method |
| UV Resistance | Yes | — |
| Ozone Resistance | Yes | — |
Compliance
- UL 94 V-0 — Compliant (Meets at third party lab)
- UL 94 HF-1 — Compliant (Meets at third party lab)
- Environmental seals against dust, moisture, air, and light penetration in outdoor enclosures including lighting fixtures, HVAC units, and electronic cabinets requiring higher closure force resistance
- Durable, high-closure-force gaskets for enclosures where standard-compliance sponge grades cannot maintain adequate sealing pressure
- Environmental sealing in assemblies subject to higher mating flange loads or vibrational loosening of the sealed joint
- General environmental sealing requiring UL 94 V-0 and HF-1 rated firm silicone sponge
- Replacement or alternative sealing for HT-820 applications
Common industries: Electronics, HVAC, transportation, industrial manufacturing, outdoor enclosures.
BISCO® RS-820 is a firm-grade cellular silicone sponge in the BISCO® RS series, positioned as a direct alternative to HT-820. It shares the same lightweight cellular silicone sponge construction as the series but is formulated to a higher deflection resistance — 22.5 psi CFD — for applications that require a more durable, high-closure-force gasket.
Available in 1/8″, 3/16″, and 1/4″ thicknesses, it is suited to environmental sealing in outdoor enclosures, electronic cabinets, and HVAC units where greater mechanical resistance to compression is required to maintain the seal under higher mating flange loads.
The material achieves a compression set of 4.0% at 22 hours, 212°F, 50% deflection per ASTM D1056, consistent with good long-term sealing performance under sustained load at elevated temperature. Low temperature brittleness is rated at -67°F per ASTM D746, consistent with the full temperature range of -67°F to 392°F. Water absorption is 1.0% per ASTM D1056. UV resistance and ozone resistance are both confirmed Yes. The material exhibits temperature independency across its service range as stated on the TDS.
Compliant with UL 94 V-0 and UL 94 HF-1 (meets at third party lab).
What differentiates RS-820 from the other grades in the BISCO® RS series?
RS-820 is a firm-grade cellular silicone sponge at 25 lb/ft³ and 12–20 psi CFD, one grade below RS-840, and significantly firmer than RS-800 (25 lb/ft³, 11.5 psi CFD) and RS-870 (16 lb/ft³, 5 psi CFD). RS-820 is available in three thicknesses (1/8", 3/16", 1/4"), whereas RS-840 at the same hardness level is limited to 1/8" and 3/16". RS-820 is specifically positioned for enclosures requiring a more durable, high-closure-force gasket, and is an alternative to HT-820.
Why is compression set critical for a firm cellular silicone sponge used in high-closure-force sealing?
In firm-grade sponge sealing applications, the material is typically installed under higher flange loads than softer grades. Compression set determines whether the sponge will maintain its geometric recovery and contact force against the mating flange after sustained compression at elevated temperature. A firm sponge with high compression set will permanently flatten under the higher applied loads of its intended applications, losing the sealing force advantage that distinguishes it from softer grades. RS-820's compression set of 4.0% at 22 hours, 212°F, 50% deflection per ASTM D1056 confirms the material maintains its sealing geometry across the rated service conditions.
What is the temperature range for RS-820?
The temperature range is -67°F to 392°F as listed on the TDS. Low temperature brittleness is rated at -67°F per ASTM D746.
Is RS-820 suitable for flame-rated environments?
Yes. RS-820 passes UL 94 V-0 and UL 94 HF-1 at a third-party laboratory as listed on the TDS.
How should RS-820 be specified?
Specify grade (RS-820), thickness (1/8", 3/16", or 1/4"), color (Gray), applicable compliance requirements (UL 94 V-0, UL 94 HF-1), dimensional tolerances, and finished format (sheet, slit roll, or die-cut gasket).
