I nicknamed this bag the "freezer bag" I used it with the uninsulated Big Agnes pad and froze my ass off in 50 degree weather. Unless you're using the q-core pad, this bag is only suited for hiking Appalachian Trail south of he Mason Dixon Line in June through Mid September, or in tropical climates.That said, it is light weight and packs down into a very small package. Generally speaking the Big Agnes sleep system concept is great, and this bag is very comfortable as long as the weather is warm and humid.
Used this bag many times paired with a BA Insulated AC. Comfort range for me is >50 (w/ a decent base layer), but have camped out down to 41 with a midweight base layer and bag liner.The area of primary concern was in the foot box area. I consider myself a mildly cold sleeper, but would probably rate this bag no colder than 50 degrees.Before making this purchase I was looking at the Therm-A-Rest Tech Blanket, but believe this was a better purchase. Very spacious, relatively light, and packs small.