Gardenville, nice work! I've never seen Cuben fiber up close but I remember when you made that bag and wondered how it's performed since? Does the cloth breath? Any condensation issues?
Thanks Dryer for you comments and questions.
1. Does the cloth breath? No, Cuben does not breath, but you can build in ways to vent your Cuben items.
2. Any condensation issues? Almost no, I slept in the bag a number of times with nothing on to see what it would be like. The only condensation was just a very little dampness on my feet and that evaporated very fast when I got out of the bag. It was about like you might expect if you had a VB liner inside your sleeping bag. I have used it on my bed at temperatures up to about 65 degrees to see how it would react at a higher temperature with about the same results. The Cuben bag seem to work best for me if I am wearing silk weight capilene underwear or something about that light. As with any VB item I want to be just on the cool side and I have no problem with condensation. I keep my house heat set at 60 F and when it gets a bit cool the Cuben Bag is the first thing I grab to sleep in. I just don't close it up tight. I made the "slide-in" opening larger to make getting in and out easy and I use that as a vent of sorts to keep from getting to warm.
I have been happy enough with the all Cuben Sleeping Bag that I am planning another version of it that should weigh at or under 16 ounces. The new Cuben bag would not have an insulated hood or yoke. I expect to use an insulation in the 2.5 to 2.6 ounce per square yard range so it will work down to something under 40 degrees "F". The bag would be used as a Spring time or early Fall sleeping bag.