RS-840 Very Firm Silicone Sponge — Technical Overview & FAQs

Product Overview
RS-840 is a very firm closed-cell silicone sponge designed for the highest performance sealing, gasketing, and load-bearing applications. It retains foam-like lightness but delivers sealing capabilities similar to sponge rubber. It is suited for applications with high compression force requirements, mechanical stress, environmental exposure, and thermal extremes. Operating range spans from about -67 °F to +392 °F.

Key Properties
Typical density is approximately 30 lb/ft³. Compression force deflection is about 22.5 psi (ASTM D1056) for common thicknesses. Compression set is around 4% after 22 hours at 212 °F and 50% compression. Water absorption is near 1%. The material meets UL 94 V-0 and UL 94 HF-1 flame ratings, resists UV and ozone, and maintains performance under heavy mechanical load.

FAQs

What is RS-840 silicone sponge?
RS-840 is a very firm closed-cell silicone sponge engineered for sealing and gasketing where very high closure force, structural integrity and environmental durability are required.

Where is RS-840 used?
It is used in outdoor enclosures, high-closure-force gaskets, press pads, lighting and HVAC units, electronic housings, and transportation systems requiring robust sealing under load.

What makes RS-840 stand out?
It features high density (~30 lb/ft³), high compression force deflection (~22.5 psi), low compression set (~4%), wide temperature tolerance and flame rating. It resists UV, ozone, water ingress and long-term mechanical stress.

Is RS-840 suitable for custom fabrication and adhesive-backing?
Yes. Like the rest of the RS series, RS-840 is available in sheet, roll or tape form, can be die-cut into custom gaskets or pads, and is offered in adhesive-backed versions for installation convenience.

Request RS-840 samples, data sheets or custom fabrication support from H-O Products - contact us.