Sensationnel Goddess Remi Fusion Silky are 25 strands. Fusion is generally the preferred method as fused hair extensions can last up to three to six months with skilled application and proper care. Hair extensions can be attached to your head in many different ways. Fusion hair extensions can be applied in different ways: hot or cold fusion. Hot fusion or bonding uses hot glue to attach extensions to your hair. This is the more traditional method. While it does have many happy followers, others say that the glue causes the extensions to feel stiff and unnatural. These extensions can last up to 4 months.