Lining footbox with thinlight

Yes,but probably not to the extent you will want.

I used my 40 f quilt at 28F one night. It was a long cold night, 34 F at 8 pm. My feet were very cold. Wrapping them in my rainjacket produced a noticeable change. Probably only 1-2 F, but I could feel it.

You will not regret bringing down booties when its cold if you get cold feet. A warm good nights sleep makes all the difference in a trip.

You might try a good thick pair of wool socks. Lots cheaper than down booties, and at 30 degrees they're good enough for my cold feet.

Yep, good, thick, loose wool socks that are used for just sleeping in (so as to keep them dry and clean) are definitely the cheapest way to go.

Another trick is to use vapor barriers on your feet. Vegetable or bread bags are super light and free. Place them over thin liner socks, and then your thick socks over that. This will add a good fifteen or twenty degrees to your comfort zone.

Hope it helps!

You could try acorn fleece socks which should be warmer for the weight than wool socks.

My feet get cold VERY easily. I found vapor barrier AND down booties are required when it's in the 20s and I am trying to sleep. Used Mylar-type shipping bags work well for me and they double as dry storage bags when on the trail.

My question: what exactly is "thinlight?"

"Thinlight" is 1/8" CCF.