I like clear plastic - chickens can see out and get maximum light in the winter, and I can see in!
This is our third winter with chickens, and I invested in 30 mil marine vinyl tarps for most of the run this year. I thought about doing marine vinyl roll by the yard and putting in my own grommets, but the tarps are soooo much easier and about the same cost.
Also
Reusable zip ties are the BEST! I hammer cable staples where I need them and zip tie adjust the tarps where I need them! One nice thing, too, is that as the temps change and the tarps expand/contract, I can adjust the zip ties as needed. I haven't gone through a winter with them, yet, so we'll see how they hold up. They're cheap enough that even if I get a season's use out of most/some of them, they'll be worth it.
Another plus to the reusable zip ties and tarps is that I can fold the tarps up or down in changeable weather for extra ventilation/airing out of the run. I attach the top grommets back to the run high enough so that the vinyl doesn't crease in the cold. Growing up we had a boat with marine vinyl, and one rule was to never fold it - always roll it, lol. Keeps it from cracking.
I can go one grommet row or two down, depending on how warm it is. My cable staples are all there and I have a reusable zip tie in each one, so raising and lowering the tarps is super quick and easy.
I will probably add a few grommets in the gaps (see left side of pic) next year for the really cold, windy, snowy depths of winter, but overall, I'm very happy with this setup.
Just a side note - as I need to replace tarps (which shouldn't be for several years), I'll probably go with the 4x6 tarps. They're just easier to handle and store overall, and ventilation can be a bit more fine-tuned.
Added plus - I can do all the winterizing without my husband's help and on my schedule

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The tarps came from here (various sizes and also 10 and 20 mil available):
https://thetarpswholesaler.com/6-x-8-heavy-duty-30-mil-clear-pvc-vinyl-tarp-mp-906
The reusable zip ties came from here:
https://www.amazon.com/dp/B078P7KRM4?psc=1&ref=ppx_yo2ov_dt_b_product_details
Cable staples came from here:
Gardner Bender 1/2 in. Metal Cable Staples, 50-Pack