> wool would probably would be OK as a top insulation layer under cover.
While I do put foam boards on top of my hives in winter, I don't think people are thinking clearly about the value of insulation. Say you insulate your house to the maximum, but decide to leave the front door open. How much value does the insulation have? More insulation isn't going to make the living room warm if the door is open. You need to put on an overcoat or even a blanket.
This is what the bees do: they form an insulating blanket of live bees. Any heat that escapes is due to the inefficiency of the bees. Heat may escape from the top of the cluster but they don't want that. They are not trying to heat the cavity.
So insulating the top is probably of minimal use. Perhaps it reduces condensation on the top of the cluster, IDK, I haven't seen condensate nor ice crystals on a cluster in many years.
PLB
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