I wouldn't worry too much, it is only in the last decade that keeping bees warm has become fashionable. For twenty years before that I never gave my bees anything but matchsticks under the crown board! Never lost bees to cold. The food keeps them warm, enough food and they will regulate what they are given to suit them.
E
Fashionable ... perhaps .. but there were a lot of well known beekeepers who realised a long time before this that keeping bees snug over winter was a good idea ..
Bill Bielby (well respected Yorkshire Beekeeper) said in his 1972 Book - Home Honey Production :
Page 43
"Losses of heat mean losses of honey;
thus, good insulation of hives is
essential. Through air currents carry
away heat and neutralise the benefits
of insulation. Just like every other
animal, the well-being of bees depends
on warmth and comfort, protection from
the elements and an adequate supply of
food. "
and Page 44
"For most economical wintering, hives
should be highly insulated and com-
pletely draughtproof . "
50 years on and there are still some beekeepers who remain unconvinced of the benefits of insulating and draughtproofing hives.
Was Bill Bielby ahead of his time .. who knows ? William Broughton Carr was well before him (Another Yorkshireman I might add !) and he advocated filling the space in between the lifts and the brood boxes in his WBC hives with straw for overwintering ...
If modern insulation materials had been available when these pioneers of modern beekeeping were around I feel certain they would have been extolling the benefits of Celotex/Kinsgspan/PIR etc.
Home Honey Production - available on ebay for as little as £2.70 and well worth a read ..
https://www.ebay.co.uk/itm/Home-Hon...396631&hash=item440df47464:g:Tz4AAOSwXjFZ4HGp
OR ... The text is available on line ...
https://archive.org/stream/Home_Honey_Production/Home_Honey_Production_djvu.txt