In sheep wool, the cellular structure includes 2 types of cells:
are curved in shape, allowing the fibre to be stretchy and elastic. Cuticle cells, are on the outside of each fibre taking the form of spines, which hook onto other fibres as they pass by – therefore matting and tangling the fibres, and containing them to form one long line.
In other fibres, like most dog and cat fur as well as human hair, this is not the case. The fibres are usually various lengths and of a smooth outer texture, which allows plenty of ‘slip’ and the fibres slide past each other instead without gripping. This yarn will have no structural integrity.
Blending in a bit of wool fibre with the desired fibre and spinning the two together will overcome this problem. The wool fibre traps the other fibre within its spin. As the fibres are passing each other, the non sheep fibre will be contained in the hooks.
A familiar example of this would be the famous possum/merino blend from New Zealand. Both fibres are of similar fibre diameter and the very short possum fibres are trapped by the merino ones, giving a lovely, even pale grey colour in the extremely warm finished product.