My eleven-year-old daughter has a detailed mandate from her school on how to. Jun 25, 2017. Kei says that split ends cannot simply be bonded or “glued” back together. “Your hair is made up of three parts – the outer layer, called the cuticle, the middle layer or core, called the cortex, and the inner layer, the medulla. The cuticle holds and binds the cortex, protecting everything that's inside it,…