To the Colorado river, and back
The bag served me well for four nights in March in the Grand Canyon. During the coldest night when the temp must have been around 20F, judging by the cooking water which froze on top, my feet got a little cold, but I was using a short pad and no tent. To my surprise the bivy-bag I had borrowed leaked like a sieve, so my Cat's Meow got soaked one night. It dried out in no time in the sun the morning after. I was relieved I had chosen synthetic fill.