1. Hair Cuticle must be present

Mother Nature provided hair with a scaly coating known as the "cuticle". The cuticle acts as a natural protection and is responsible for the shine and resilience of your hair, locking in essential moisture and protecting the hair against the harsh elements (wind, sun, pollution, etc.) to which it is exposed. Hair without cuticle would rapidly dry out, become brittle and break, and appear lifeless and dull. (For reasons which are explained later, cuticles are removed from an available source of inferior quality hair.)

2. Cuticle scales must face the same direction

In your own natural growth, the individual cuticle scales are naturally aligned in the same direction. Hairs next to each other are easy to comb because of this. But what would happen if the cuticle scales where not all facing the same direction? Imagine a Velcro fastening. The reason the fastening grips so well is because the burrs which interlock with each other are all aligned in different directions. This is clearly the opposite of what is required for hair extensions because, in this case, interlocking would soon lead to completely matted and tangled hair.

3. No mixed cuticle and non-cuticle hair

When combed wet, natural hair with cuticle will stretch by approximately 10%. Hair in which the cuticle has been removed (later explained) is much more elastic. Because of their different stretch, mixing these two qualities together can produce disastrous results, especially in the case where the cuticle has not been fully removed from the inferior quality hair and may be facing in the opposite direction to that of your natural hair.

4. Hair diameter must not be thin

The hair of typical European women has an oval cross-section and is relatively thin; it is normally between 0.06mm and 0.09mm thick. The hair used for hair extensions must have the same characteristic in order to provide easy maintenance and a lasting natural appearance and feel.