Cracked windshields are repaired using resin. Resin is made of acrylic acid. Think of resin as the glue that holds the crack together to prevent further damage. The type of resin you use depends on whether the crack in your windshield is small or large, shallow or deep. Resin Viscosity There are many types of resins on the market. If you are going to fix your windshield on your own, the first thing you must determine is the extent and depth of the damage.