Prestone Radiator Stop Leak features a patented formula that quickly stops leaks in radiators, water pumps, and heater cores while also protecting against pitting and corrosion. Prestone Radiator Stop Leak takes sealing performance to a higher level by both stopping the leak as well as the corrosive condition that causes leaks in the first place. Its unique combination of natural and synthetic components provides the ability to seal leaks up to 0.020-inches x 0.5-inches. What makes this possible is the size, strength, and durability afforded by fibrous particles, the same materials in bulletproof vests. Prestone Radiator Stop Leak particles have been chosen to seal even large leaks without interfering with the flow through the radiator and heater core tubes. It also boosts corrosion inhibitors to protect against pitting and corrosion, which cause radiator leaks.