Pre-bonded hair extensions are hair strands that have been bonded at one tip using an adhesive like keratin and glue. These extensions come in different types such as nail-tip, stick tip, and nano-tip hair extensions. Nail tip is also called fusion hair extensions because they are attached to the natural hair using a heat connector. For this extension, heat is needed to melt the glue and attach the strands to the natural hair at the root.