Auto windows, such as windshields, need to be properly attached during installation. Many sealants are available, from butyl rubber to urethane, but some work better than others. Safety is the key component in choosing a sealant for this front glass.
Butyl rubber was used prior to the 1970s to attach windshields. As technology advanced, better sealants were found to survive the harsh wind effects and sun damage applied to the vehicle.
Though slow to dry, butyl rubber does have significant strength to hold auto glass. But urethane has more strength and can last longer in the weather elements. In fact, the government has deemed it the specific sealant needed to pass regulations when installing or replacing a windshield.
Vehicle stability in newer cars relies in part on the structure of the windshield, so keeping the windshield free from cracks is crucial. This stability is due to the need for having lighter cars to save on gasoline consumption, where the frame is no longer the core stability source of the vehicle, but the surrounding shell is.