He appeared to be using polythene as a crown board. It's a technique I recall noting on a video, from I think Eastern Europe, that used poly hives. It made inspection a bit quicker - just pop off the roof, roll back the plastic. Any idea if it's in common usage in UK commercial honey production and any thoughts on pros and cons?
I'm using a sheet polythene under the roof on a number of my poly hives these days. It means the roof lifts off without any noise and you can then peel the polythene slowly back and the bees are hardly disturbed. They do build bits of comb between the frame top bar and the sheet but this isn't a problem. A bee farmer I was with earlier this week was also using polythene sheet under the roof on all his poly hives.