BA bags require a pad. There is no insulation on the underside of the entire bag (rectangle bags) or torso (mummy bags). The Blackburn is a great bag, and ridiculously light for a 0 deg., but it would be too warm for me most of the time. I would think the Zirkel w/ a liner and/or cover would be more versatile. But that would be for me. If you are a really cold sleeper the Blackburn might be perfect.