Leather Library
Soft, breathable, and usually left with the wool on — built for comfort, not combat.
Sheepskin is the tanned hide of a sheep, and in boots it's almost always used with the wool still attached — a different thing from the "hair-on-hide" look of a fur-on cowhide, which has its own library entry. The hide itself is thin and light, thinner still when it comes from a lamb rather than a mature sheep, and it carries natural lanolin that gives it a soft, self-cleaning, mildly antibacterial quality straight from the animal. It's naturally breathable and genuinely temperature-regulating, which is the whole reason it shows up in boots at all.
Mostly as a lining material or in full shearling-style boots, where the retained wool provides insulation and a soft feel against the foot rather than structural durability. It's not a leather asked to carry the weight of the boot's construction.
Keep it away from soaking — sheepskin doesn't tolerate heavy water exposure well. Clean with a soft, dry cloth, or lightly dampened with warm water if needed, and use a conditioner formulated for delicate leather, tested on a hidden spot first. Store flat in a cool, dry place out of direct sunlight.