As a beginning fly fisher or tier, you will note the GRHE or some variation of the very popular/productive Gold Ribbed Hare’s Ear. The tying process often involves selecting a small plastic bag, off a hook, which contains rabbit fur or a blend of rabbit fur and a synthetic. The primary appeal of the fur is the guard hairs amongst the fur, which when applied or dubbed to the hook creates a spiky appearance. All this fur, in fact, comes from a Hare’s Mask. The fur is longer about the cheeks and quite short up near the ears. The masks are offered in dyed colors with the natural mask still the most popular. I am not sure there is any advantage to buying the mask as opposed to plucking that bag off the hook. But, if you like the more hands on effort at dubbing and blending, it is always interesting to buy a mask and see what you create. Store the mask where moths or mice cannot get at it (sound advice for all your materials).