Strands of the extensions are bonded to your hair using a keratin-based bonding polymer and heat (and because chemicals and heat are used during the bonding process, this process can cause some hair loss and breakage). Extensions applied by this method generally last for two to four months. Hot-fusion-bonded hair extensions are nearly invisible, and while wearing them, you can still wear your hair up.
However, you should be aware that the bond should only be removed by a professional. Therefore, the removal is an additional cost, and it will also cause stress on the hair.