It takes a special polyurethane to form the bonds and seals around windows and glass. Moisture must be sealed out completely, yet flexibility is paramount to ensure a seal that won't dry out, withstands pounding and vibrations, and protects the glass. 3M™ Polyurethane and Hybrid Adhesives & Sealants and 3M™ Primers and Cleaners for windows and glass are specifically formulated for the unique characteristics and requirements of structural glass bonding and window glazing. Strong yet flexible. Crack resistant. They're ideal for structural windshield installations, PMMA windshield applications, hard-to-bond polycarbonates and acrylics, and flush-mounted glass for both marine and automotive use.