The Fibreskin heads also have some color variation to make them look skin-like. Although they have some variation in texture, if you've got a head of uniform color (excluding the players' grime) that's rough on top and smooth on the bottom, it's probably not Fibreskin. Also, as a modern product, don't Fibreskin heads mostly come labelled as such down by the tailpiece?

~ Becky in Tucson