Possible repurposed insulating materials for greenhouse use

I want to add a water-proof insulating blanket to my greenhouse. It needs to be fairly strong, UV resistant, and come in fairly large sizes. I'm trying to think of the kinds of things that could be repurposed for this.

So far, I've thought of insulated pool covers and thermal curtains for warehouses.

There are some folks who post on craigslist with
all kinds of used and surplus stuff like that:
https://desmoines.craigslist.org/mad/d/used-poly-iso-insulation-sold-as-bunks/7261760233.html

You might also look for concrete curing tarps.  They're weatherproof and insulated to keep concrete from freezing before it cures on big jobs.