In article , Franz Heymann
writes
Why do polythene tunnel covers need to block UV radiation?
Surely the same plants, growing in the open thrive the full dose of UV
radiation?

I think you may have a point there. I suggest that you advise the
suppliers of poly-tunnel covers that they have it all wrong and tell
them what material they should be marketing.
--
Alan & Joan Gould - North Lincs.