Sheepskin
Sheepskin comes from a mature sheep, it is thicker. It is well known for its extremely softness and durability which allows it to withstand heavy use.
Sheepskin vs Lambskin
On the other hand, Lambskin is the hide of young sheep, usually less than one-year-old. It is soft and supple. It is also thinner than sheepskin due the fact that it is taken from younger animals.
As a general rule of thumb, lambskin is best for leather garments (jackets and coats) because its soft texture easily forms to the body,