Keratin fusion hair extensions are a type of semi-permanent hair extension that involves bonding small sections of extensions to natural hair using keratin, a natural protein that makes up the structure of hair. The extensions are attached using a special heat tool that melts the keratin bond, allowing it to securely adhere to the hair strands. This method creates a seamless, natural look, allowing for flexibility in styling, including updos and ponytails.These extensions are popular due to their durability and natural appearance. They can last from three to six months with proper care, making them a long-lasting option.