If it takes an ounce of 800 fill down to fill 800 cu in, does Montbell measure their loft (to get bag rating) in the streched, relaxed, or intermediate condition. If they measure the loft to get their rating when the bag is in the relaxed position, then it seems to me that if the bag were to be strected there would be more area and the loft would decrease. How does this work? I had a 'Stretchy Legs' bag that mountain hardware made- and one that Sierra Designs made, so I familiar with how the bags work. Just wondering how Montbell figures their loft. I am looking at a 30 degree bag and my search shows that owners are happy with theirs. I plan to use this below 30 degrees and compensate with clothing.
Something that specific, I think you should ask MontBell directly.
But suffice to say that reading user feedback over the last few years, it's been fairly consistent that MontBell bags are rated pretty accurately for the "average" sleeper -- as WM bags are rated conservatively. That hopefully will give you a general feel.
I have been reading about them for some time. I have a WM now and am very happy with it. But am considering getting something new to shave some o z's. I think the Montbell stuff is priced better. Anywho, the stretch bags I had before were both synthetic and jsut thought someone might know the tech specs on this. It might be a little critical, at least for some degree of comfort, since I plan to push this bag past the limits.