Mike,
I'm glad you liked it! Most people have initially been concerned about the noise of the Tyvek. I certainly think a tent or tarp out of Tyvek would be very loud. However, a Tyvek bottom doesn't make much noise when you are laying on it. Can't say the same for my NeoAir!
As for the room inside, I roll over a lot during the night and this bag makes it easy. I also sleep most nights with my bag over me like a quilt. Being free from ants and mosquitos with my sleeping bag open is great. I also like having my gear out of the weather. I've had 1-man tents with much less room for gear.
I share your concern about a white bivy in snow. We might need a bright streamer to find our camp. Maybe some reflective tape would be a good idea. I really wanted to have a bright color, but the manufacturer said it would reduce the breathability of the fabric. I went for the most breathable I could get after suffering from ice in my GoreTex bivies.
If you take care with the lightweight fabrics, it will serve you well.
Thanks,
Dave
