Wrapping hivea in winter is less about insulation of the hive, but more about protecting the hive from the weather.
If you really wanted to insulate the hive you would usw styrofoam or similar. But with wood there is one problem, it absorbs water, this water has to be driven off in the spring. The bees do that by heating, and that costs lots of energy. With the wrapping, you protect the wood from absorbing water, at least a little bit and specially in spring from reabsorbing.
If you treat your hives in boiling wax, the wood can't absorb water anymore.
Also styrofoam hives win in spring because if that, less because of the insulation. I recommend you, to put a couple thermomethers into your hive in spring, you will wonder how cold all the frames are in which the bees don't breed. They are really genuie in insulating the cluster with there bodies.
With wooden hives only painted or oiled, the the temperature towards the wall if the crowded frames is about 5?C less while the walls are still wet and you can easly See where the cluster is located, from the outside, due to the dry wood stains.