Silicone - Viracon - Single Source Architectural Glass

Viracon’s insulating glass units configured with aluminum and stainless steel spacers are constructed with a dual seal configuration where polyisobutylene (PIB) is the primary seal and structural silicone is the secondary seal.

PIB is the primary seal of the insulating glass unit preventing moisture vapor transmission into the unit’s sealed space. The silicone secondary seal acts as the adhesive that holds the unit together in both conventional and structurally glazed systems. Both the PIB and structural silicone must maintain adhesion to the glass and spacer throughout the life of the unit.

Silicone is uniquely resistant to ultraviolet light and is the only sealant capable of being exposed long term to UV, temperature extremes and harsh atmospheric conditions. The high strength of silicone makes it ideal for structurally glazed applications.



Viracon’s insulating glass units configured with VTS are constructed with a single component spacer consisting of a black thermoplastic with integrated desiccant and polyisobutylene (PIB). VTS is chemically bonded to the glass and to the secondary silicone sealant, eliminating the need for added vapor barriers, acrylic adhesives, additional desiccant or PIB


All insulating units have a sightline.  The sightline is the edge dimension of the insulating glass unit covered by the spacer.  Insulating glass in a conventionally glazed system typically utilizes a 1/2″ sightline.

The sightline for insulating glass in structurally glazed applications must be calculated based on the unit size and wind load.  This ensures there is enough silicone to glass contact to appropriately support the insulating unit and exterior glass ply when the glass is under load. Sightlines are calculated based on ASTM C1249 Standard Guide for Secondary Seal for Sealed Insulating Glass Units for Structural Sealant Glazing Applications.

Viracon offers a Deflection and Sightline Reference Guide to assist in identifying the appropriate sightline based on glass size and load. Contact Viracon for sightline requirements specific to your project.


Black is Viracon’s standard sealant color for insulating glass. When black is specified, both the PIB and silicone will be black. Please note, the color of the PIB and silicone materials are not identical due to material differences and will be distinguishable.

Viracon cannot guarantee the future availability of component parts manufactured or supplied by others that are incorporated into Viracon products.