I have a bag that is at least 4" in loft but is rated at 20 degrees. What's up with that?? I did not realize that the bags were rated that way. That is very interesting. Does it work the same way for down bags and synthetic ones too?? I would be interested in knowing that. I have a western mountaineering bag and I also have a Marmot bag. They both work really well but the western mountaineering bag is the better quality bag in my opinion and is, although rated the same the warmer bag also...sabre11004...