Fusion extensions are preferred for their long lifespan and better bonding with the natural hair, despite their higher cost and effort. This is also because fusion extensions look more natural – they “fuse” with the natural locks and do not leave any signs of attachment. Fusion extensions are applied as cold fusion extensions or hot fusion extensions. In cold fusion extensions, an ultrasound device is used to attach the hair extensions to the natural hair. The glue in these fusion extensions is a polymer with a keratin base. Cold fusion extensions do not cause any untoward stress on the hair follicles. Hot fusion extensions are applied by a heated rod which bonds the hair extensions to the roots of the natural hair. While these fusion extensions last longer than other hair extensions, including cold fusion extensions, they can only be used where the natural hair is thick and strong enough to withstand the heat treatment process. To get the best results from any fusion extensions, regular grooming and maintenance are required. The maintenance schedule also involves re-fusing the hair extensions at least once every 3 months.