>In videos I've seen, many UK beekeepers use some kind of flexible plastic (it looks like plastic, dunno for sure what it is) for their regular hives. How do these work?
They are just thick Visqueen http://www.packagingsupplies.com/Poly-Sheeting-Visqueen.html
they work like any inner cover creating a slight airspace to reduce condensation. The orginal inner covers were quilts hence the term still used in some places of "quilt board".
> Do they sit directly on top of the bars?
> Wouldn't that hinder ventilation?
It doesn't seem to.
> Do they keep the bees from traversing the top of the bars?
> Does Michael use these only in nucs, and why?
Yes. To keep the multiple nucs from spilling into other nucs in the same box when opening them to inspect. Without them queens often get killed by the bees from the nuc next door spilling over.
>On a related note, I've seen canvas covers for use in hive inspections. They have a frame-width opening in the center so you can pull a single frame and keep the others covered. Anyone have experience with these?
Yes. But they are a pain to haul around and my bees are calm enough that they are usually not useful. The few hives that they might be useful in, I'm busy requeening, in which case they don't help that much anyway.
> When I inspect I do it as quickly as possible, for 2 reasons: one, I want to disturb them as little as possible, and two, I still find all those bees crawling around somewhat intimidating smiley What I miss because of this (fear, mostly) is a thorough inspection -- maybe the covers would make me feel more comfortable, and disturb the bees less?
They will disturb the bees less, but only moderately less. A top bar hive will give you even better results.