How do you insulate or add R-value to existing walls? Larry Janesky from Dr. Energy Saver demonstrates the process of using injection foam insulation in the exterior walls of a home with vinyl siding. Injection foam can be applied to walls even if they are already insulated with fiberglass batts. Besides increasing R-value, injection foam also closes gaps in the structure and seals air leaks. Injection foam insulation can be applied with less disruption than other conventional methods, even in finished and vinyl sided walls. In this particular case, pieces of the siding were removed, holes were drilled to apply the foam, and the vinyl siding was replaced afterwards. Injection foam is a water-based product with no toxic fumes or harsh smells.