I have wrapped with fiberglass (covered with plastic sheeting), and with tar paper. In both cases hives have survived fine - of course, hard to say which the bees may have preferred!
In any case, I close the opening in the inner cover once it is in winter position, and put an empty super above it in which I put a bat of 3 inch fiberglass. I am quite sure that this is worth doing - on the occasions that I have put my hand under that insulation in mid-winter, the inner cover is warm as toast. That keeps water from condensing on the inner cover and dripping down on the bees, and the opening in the inner cover allows moisture to escape. In early spring, I can open the inner cover hole and put in a feed bucket which I then wrap in insulation. The conserved heat keeps the syrup warm so that the bees will take it readily.