I have stuff that is for polytunnels that I bought online a few years back. It allows UV through and is very tough. Not sure if it is meant to keep the heat in but when you lift the section up the heat comes whooshing out but I'm pretty sure it would do that with any kind of cover over the area. I can't remember exactly how much it was (there was a thread on here at the time saying I was ordering it) but £17 rings a bell and with delivery think it was £20 odds. You had to get the full length which I kind of think was 24 feet and possibly 2metres wide. It will all be on here somewhere. I have it stapled to a wooden frame over the wire mesh
