This CRL Dual Seal Insulating Glass Starter Kit has all the components necessary to fabricate double seal I.G. units. Polyisobutylene which is a one-part, non-drying, non-hardening ribbon material with exceptionally low vapor transmission and non-fogging characteristics, forms the primary seal. Insulating Glass Silicone, applied with a standard caulking gun, specifically formulated for bonding and sealing I.G. glass units, makes the secondary seal. The Double Seal Spacer is grooved on the shoulder, allowing it to accept the Polyisobutylene tape, while the taper below the shoulder will accept the silicone secondary seal.