Fill-It Flexible Wood Filler is the perfect partner to Smiths CPES for restoring wood. It is the Epoxy Wood Filler that lasts offering a permanent and watertight solution. It will flex with wood and is so waterproof it can be used below the waterline. Smith's 2-Part Fill-It Fairing was invented by American Scientist & Aerospace Engineer Steve Smtih in 1972.