Wool fibers are mostly composed of alpha-keratin, present in the hair of all mammals as well as in the horns and claws. The cells of their outer layer (cuticle) have evolved to overlap like small shingles. Inside sheepskin there are two types of follicles that produce wool: primary and secondary. Primaries develop within the lamb’s skin before birth, are larger than secondary follicles and therefore tend to develop thicker and longer fibers. The secondaries, on the other hand, are smaller and much more abundant than the first type. Their number, however, is strictly dependent on the conditions following childbirth.