The scales form a ratchet- like structure resulting in a directional friction effect, with the fibres being smoother in the direction of growth.
Thai ratchet-like structure of the scales during the growth of the fibre interlocks with the structure of the scales sheath of the follicle.
This inner root sheath structure moves forward with the fiber as it grows outwards and supplies the mechanism by which the keratin fibre is anchored on the sheep's back or on the human scalp.
Pulling out a hair 'by its roota' actually results in tearing away at the inner root sheath in the follicle.
This directional friction effect is the basic factor in the entanglement of fibres involved in the felting and shrinkage of untreated wool textiles.
On the sheep’s back, because the scale ratchets are all aligned in the same direction, entanglement of fibres in a wool staple rarely occurs.