Cold fusion is also known as micro link, micro loop hair extension. It is a strand method that is applied by weaving small sections of hair through a micro link tube. Cold hair fusion extensions were created to be a gentle alternative than hot fusion hair extensions. Hot fusion, also known as keratin hair extensions and tip hair extensions, is another strand method attached at the keratin based tips with a heating element.They are applied to your natural hair in small ‘bundles’ with a heated keratin adhesive.