Bondo Short Strand Fiberglass Reinforced Filler empowers DIYers to tackle the toughest rust repair jobs via the strength of Bondo fiberglass strands. This thicker formula is stronger than Original body filler, dries fast and works great on vertical surfaces like car doors.Bondo Short Strand Fiberglass 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.