"Skins" for skis (Berry Lane Estate WD3)

I thought I had cleared all of my husband's old skiing things but have found some "skins" for attaching to skis, when skiing uphill, I think. (He did a lot of ski-mountaineering years ago.) The bag is labelled Montana Adhesive ski-skins and there is also some "adhesive to re-coat self adhesive skins." I am not a skier and have no idea whether they are still used, or whether these are completely out of date now. But you are welcome to them!