Is expanding foam watertight? Yes, some expanding foam is designed to be waterproof. Certain products are even made specifically for building ponds, fountains, and other outdoor water features.
Does expanding foam stop water? Using expanding polyurethane foam is one of the best ways to stop water leaks because the foam will expand into the cracks and help prevent future leaks. Expanding foam bonds to any type of surface and will quickly and effectively solve your water leak problems.