Climbing skins are strips that attach to the bottom of Nordic, alpine touring or randonnée skis to help while ascending backcountry slopes.
[1] They are typically made from nylon or mohair or a combination thereof, and are designed to let the ski slide forward on snow but not backward.
Attuned to maximizing the use of their materials, one outcome of their innovation was the use of animal skins to gain traction in traveling.
Mohair normally glides better on the forward movement, but provides less grip compared to nylon skins.
Nylon on the other hand has increased durability, especially when used in harsher, icier snow conditions, or on rocks.