Our Bondo Hair Long Strand Fiberglass Reinforced Filler features strands of chopped fiberglass up to 1” long for extra strength on your toughest repairs. Tackle filling large rust holes and restoring shattered fiberglass with Bondo-Hair Long Strand Fiberglass Reinforced Filler.Our Bondo-Hair Long Strand Fiberglass Reinforced Filler features strands of chopped fiberglass up to 1” long for extra strength on your toughest repairs: filling large rust holes, restoring shattered fiberglass and more. In fact, this waterproof filler delivers twice the strength of standard body filler, making it ideal for rebuilding missing pieces during full vehicle restoration.