Bondo glass reinforced filler makes an excellent foundation for hole, dent and rust-out repairs without the need for backing strips, cloths and resins. It contains short, interlocking fiberglass strands and fibers that make it twice as strong as regular body filler. It is also slightly thicker and provides a fast drying time, making the filler less messy on vertical surfaces like car doors. Bondo glass reinforced filler provides fiberglass-quality repair of small holes and rust-outs (up to 1/2 in) without the need for backing strips, fiberglass mat or fiberglass resin. This reinforced body filler already contains the short, interlocking fiberglass strands, making it twice as strong as standard body filler and also much easier to use during vertical repairs when the filler can drip down the surface and cause extra work. If your repair needs even more strength, it also works well with traditional fiberglass repair materials and tools. The filler is easily mixed using the included Bondo red cream hardener, designed specifically for use with Bondo fillers. It also features a fast drying formula that is sandable in as little as 20 min, saving you time on auto body repairs. This waterproof filler is ideal for repairing dime size or smaller (up to 1/2 in) rusted out metal holes and shattered fiberglass body parts. It is compatible with all paint systems for cars and boats. As a brand of 3M, Bondo is well known among collision repair professionals and others who are committed to helping you restore the beauty and value to your cars and boats. This fiberglass reinforced filler is another way that 3M applies science to life and helps you rediscover the excitement of the vehicles you own.