How Do Sheep Cope With
First, the space between the hairs slows air movement.
Dramatically. One might be tempted to say sheepskin “traps” the warm air, but in realty the fleece will breath air like a sponge will breathe water – that’s to say it will “breath” – but only when outside atmospheric pressure differs significantly, like when you squeeze it.
So, we have a space full of warm, moisture rich air. This moisture would love to condense and change its state into liquid water. Everyone wants change, but real change is hard. The water molecules are so keen to condense that they will willingly give up all their energy to any wool they happen to land on. The trouble is the wool is hydrophobic. This means the wool requires more energy than the water carries by itself to let the water condense. This energy must come from somewhere.
This way the fleece either keeps the sheep dry or harvests energy from the environment. Similarly, a sheepskin will dry quickly in a tumble dryer and
feel dry to the touch. You will always have a warm dry place to rest your head, no matter what the weather is doing outside.
Shorter sheepskins will have this inner double layer and a less prominent out layer, in effect they will act as if some of the soft inner hairs have longer, flatter, tips.
The long hairs have a different profile at the base, and by the time you get to the hair tip, they appear to be different hairs altogether. The truth is the long hair is interacting with atmospheric moisture differently at different points along its length.
Long haired sheepskins retain the warm down, and augment it with at times much longer hairs. These substantially increase the bulk of the sheepskin, and distance the damp air from the sheep. These long hairs have a flat profile, ideal for evaporating condensed moisture.
These long hairs slow the ingress of moisture towards the core, whilst at the same time wicking the entire sheepskin dry.
Flatter hairs will hold a kink or a wave much better than a round profile hair. The inner hair on a sheepskin will be of round profile and fairly predictable performance during growth.
Flat hairs on the other hand can kink during growth, according to irregularity in the rate the follicles produce keratin, the protein that is hair. Sheep hair growth is affected by all sorts of things. Changes in food and weather, or a bout of illness, can stop hair growth, cause split ends, kinks and permeant waves of all kinds. See those swirling patterns on a Jacob sheepskin? That will be because of the arrival of spring, or because the shepherd’s daughter gave the ram a bag of apples.
Wild sheep grow hair coats with long outer fur that sheds itself annually. Domesticated breeds will grow their inner wool coat continuously, and the shepherd shears the sheep every year. Sheep fleece varies throughout the year. Correspondingly, sheepskin will vary. All will meet and exceed the required standards, but some will be better at shaking off a light summer shower than others. The key is to learn your sheepskin.