Arfermo,
I look at hive insulation and compare it with my house. House: Open the windows in the winter and all the warm air escapes, so I tend to keep them closed. I invested heavily in roof insulation - again to reduce my fuel usage (and therefore the cost). My wall cavities have been insulated for many years. Those insulation costs have been recouped probably several times over. The beehive is a similar entity, only bees live there.
While they may well come through the winter perfectly healthy, they will use more fuel to keep their 'house' warm. You made no mention what the store levels were before and after the winter and whether you fed them in the winter/springtime. These are all costs, as I see it. Hidden or forgotten by some.
A few pieces of insulation cost little more than a kilo bag, or two, of sugar. Your choice as to the way you wish to go. The cost of the insulation can be spread over several seasons. The sugar is more of a running cost each year. What I do know is that their winter honey store is their fuel bunker and the amount of fuel needed to maintain a satisfactory temperature is reduced with effective use of insulation.
I usually leave honey on the hive if possible. That way, there is no possibility of 'sugar honey' in my supers. Honey costs nothing that way but is worth far more than sugar, so I don't wish them to waste it unecessarily.
On top of that I have noticed that the insulated colonies get a better start in the spring (the Dartingtons are ahead of the Nationals). Ymmv, but those are the facts, as I see them; simple physics and energy balance.
Regards, RAB
