HT-840 Extra-Firm Silicone Foam — Technical Overview & FAQs

Product Overview
HT-840 is an extra-firm grade closed-cell silicone foam designed for high-closure-force sealing and gasketing. It combines the strength of traditional sponge rubber with the resilience and temperature stability of silicone foam. It’s suited for applications requiring strong mechanical stability, fire resistance, and minimal compression set over long service life.

Applications
HT-840 is used in outdoor lighting fixtures, electronic enclosures, automotive and aerospace systems, and mechanical assemblies exposed to vibration, temperature extremes, and environmental stress. It performs exceptionally where very firm sealing and load support are required.

Performance Advantages
HT-840’s dense cellular structure delivers a compression deflection around 22 psi at 25 %, ensuring tight, stable sealing. It maintains its form under load, resists UV and ozone degradation, and provides reliable performance between -67 °F and +392 °F. The foam is flame rated UL 94 V-0 and HF-1, with very low smoke and toxicity characteristics.

Key Properties
HT-840 has a typical density of about 28 lb/ft³, compression force deflection near 22 psi at 25 % strain, and an exceptionally low compression set (less than 5 % after 22 hours at 212 °F). It remains flexible at sub-zero temperatures and stable up to nearly 400 °F. The closed-cell structure ensures minimal water absorption and maximum durability under prolonged environmental exposure.

FAQs

What is HT-840 silicone foam?
HT-840 is an extra-firm closed-cell silicone foam designed for sealing and gasketing where very high compression force and long-term durability are needed.

Where is HT-840 used?
It’s typically used in outdoor electrical housings, lighting enclosures, automotive seals, and mechanical assemblies exposed to extreme temperatures or vibration.

What are the advantages of HT-840?
It has a higher density and compression force deflection than standard foams, providing structural integrity and load-bearing capacity with excellent resistance to aging and compression set.

How does HT-840 perform under heat and UV exposure?
HT-840 remains stable under continuous temperatures up to 392 °F, and resists degradation from UV, ozone, and environmental aging.

Can HT-840 be supplied in adhesive or custom formats?
Yes, it’s available in sheet, roll, and die-cut gasket forms, with or without pressure-sensitive adhesive backing.

Request HT-840 silicone foam samples, engineering data, or adhesive-backed gasket configurations from H-O Products - contact us.