POR-15 Patch Filler & Seam Sealer is quite literally POR-15 Rust Preventive Coating in a tube, and it dries as hard as a rock, remains flexible, and once dry is totally impervious to fuels and solvents. This rust hole filler is so tough it may actually add strength to weakened metal, and it won’t absorb moisture and swell like conventional body fillers. This sandable seam sealer permanently patches holes in steel, wood or some plastics, seals seams, and even fixes holes in fuel tanks. 4 oz. tube.