Also, not all "foams" are equal, or to be used in a boat. For marine applications, you only want to use closed-cell foam, but NEVER white styrofoam, which is what most older boats were made with unfortunately. The older foams used can/do soak up tons of water which sort of defeats its purpose. Most DIY folks use the 1" thick pink/blue insulation foam panels from Lowes/HD which works very well and can be removed in the future, unlike spray-in foams that expand when applied and can actually damage the hull and are a PITA to remove should you ever need to repair the hull in the future. Any holes in the hull should be properly sealed by welding them, or filling them with epoxy.