Skins are a cloth that has a texture on it like reptile skin so that it glides the split (ski or board) forward and then when you step down it gains traction so that you can effectively cross country ski on a splitboard or AT/touring ski setup. Cross country wax performs the opposite of fast wax in the sense that it grips the snow instead of releasing that surface tension. Skins basically mimic this performance but even better sortof because you can glide a little better without the sticky wax.
I haven't even used em, just trying to answer ur question, we have lotsa splitters here who can tell all and correct me.
Ah, ok! We call them "fur" and they are more like a soft short carpet.