Bivy Quilt

I have used a SOL emergency blanket, less than 3 oz. for just that purpose as well as a ground sheet..

I've been using MYOG bivy quilt for years. I think it works good. But, if you have a seperate bivy and quilt it doesn't add that much weight.

I think maybe you can make your quilt a little narrower. There's no wind blowing uner edge of quilt.

There tends to be a small channel on both sides where the quilt isn't directly against me so there's more convection.

A little different than what you are talking about, but I have been using the SOL Escape Bivvy as both my bivy and my sleeping bag. I've pushed it down to the low 40's so far. I think this product is pretty useful and has a measure of safety since it still works when wet. I also like that I can leave it compressed without ever worrying about its ability to capture heat. I just wish it was a little more roomy for a 6' guy.

I converted a MYOG quilt to a top bag, by attaching a waterproof Cuben fiber bottom. My Neoair pad goes inside:

My shelter is a Hexamid. This modification lets me leave the groundsheet at home.

I described my quilt before this modification in the MYOG forum:

http://tinyurl.com/karen4e

Nice

One possible problem is there's an air gap at the top around your neck and shoulders.

I put in a flap of insulated material on both sides to go over my shoulders and cover this gap

It's a converted quilt, so there is a drawstring (not apparent in the photo)I can cinch to get a pretty good seal at the top. And it's definitely a summer bag, so in warm weather it hasn't been a problem.

But your point is a good one, especially in cold conditions. I guess my modified quilt is more quilt-like than top bag because there is no hood.