That may apply in the case of foil used alone as a reflective barrier; if it is in contact with a warm surface it will conduct heat away and negate most of the benefits. But when attached to an insulating material such as polystyrene or even better, to PIR, the insulation behind it will resist conduction and the reflective qualities of the foil will still be useful. The radiated heat from the bees can be detected through the thickness of the walls of the hive and there is no reason why it can't be reflected directly back into it.
I was told it looses most of its effectiveness if its not the exposed/outer surface. So the insulation properties of the foil will be negligible compared to the PIR/polly when installed in a hive roof. At least going on what I was told.
But your point about detecting radiated heat makes sense too. Going on that logic it would help to put it anywhere, as you say. But that's wrong, in the wrong place it can actually make things worse, particularly a thick layer of tin foil, rather than the thin foil on a proper sheet.
I agree with your point about what kind of surface its attached to, but I was only thinking in a context with other insulation.
One reason its more effective on the surface is because if its buried below insulation, then anything reflected would have to go through then back through the insulation, so will end up heating the wall/roof rather than being reflected.
In a sunlight scenario you must see how having the foil on the surface would reflect way more, and prevent the surface heating up. Radiated heat worked in a simlar way, but to a lesser extent as more passes through.
Then there is the conductivity factor to account for, this is where it can become counter productive.
This short vid explains it well. Most vids handling the subject were far too long bu this guy does a resonble job of explaining it in under 5m.
But as said before, its widely misunderstood and misused and thermal dynamics are are very complex subject.
A lot of these things are very situation dependent too, so unless you know the exact proportions of kinds of heat bees produce and a bunch of other data we dont have it will be hard to know for sure. But I think its pretty negligible once buried in a bee hive roof and its actually the polly/pir doing the work.
But I could be wrong!
Does anyone happen to have, two hives of simlar construction containing simlar sized colonies, a selection of insulation materials, some foil and a thermal camera?
