TR
It worked GREAT!!!
Used it in a notoriously ice cold hut (it was bone jarring cold, ice on the inside of the windows) in the mountains with a lightweight sauna bag. Worked fantastic with my lightweight sauna bag and clothing layers. Part way through the evening I had to take some of the layers off (back to merino s/s top, merino tights and merino socks). Next trip, no sauna bag just the bivvy as the weather will be mild.