Originally Posted by lori
Okay, I am a cold sleeper, and the Hudson River rating is spot on for me. So your own mileage will vary.
If you look at a 20 degree Western Mountaineering sleeping bag, you will see a five inch loft - halve that (it's a sleeping bag, there's a top and bottom) and you get 2.5 inches of loft. The Hudson River and its 3 season JRB brethren have 2.5 inches of loft. Western Mountaineering is one of those brands that needs not exaggerate - it's the Lexus of sleeping bags, by the standards of most reviewers conservatively rated, and like our JRB quilts they use high quality down.
So I would say that if a quilt were adequately filled to 2.5" of down loft, it would likely be capable of the same 20-25F rating easily.
Certainly I have found the JRB Mt.Wash4 to be very conservatively rated simply based on measured loft. Like my PeaPod, mine actually had MORE loft per my measurements than rated. Temp wise, with it's 0-10F rating I can only say I was plenty warm at 10*F, because that's the coldest that conditions available to me so far. Others have taken it below zero, but that gets to the question posed by the OP: what other winter gear was being worn or used? What base layers, etc.
But when it comes to comparing to a Western Mountaineering bags loft AND temp rating, remember the dif in a bag and quilt. First of all, the hood. And I think the Jacks would be the first to say that if you are going to be really warm at 20-25*F in a 2.5" loft quilt, you probably will need a hood to go with it. Just like a sleeping bag. Although, if the quilt is long enough, for side sleeping I am able to produce a faux hood by pulling the quilt over my head and fashioning a small breathing hole.
But above all else, consider draft control, especially for larger folks. That can make or break warmth with a TQ. Zipped up inside that WM 2.5" loft bag with neck collar cinched down tight and hood closed down to a small breathing hole is one thing. Being under a 2.5" loft TQ can be another. Unless the TQ is plenty wide enough for the user ( less of a problem in the hammock), having every thing tucked just right head to toe might be a challenge.
Even if the quilt is big enough for a given sized user, if you move much some new skills will come in handy. It helps to learn to turn over with out causing even a temporary draft which allows your trapped body warmth to escape. It is also important that the quilt can be well secured around the neck and shoulders. I find a "snap" and draw string to be really helpful.
Of course most of us will learn to deal with all of the above for the many other benefits of using a TQ vs a bag in a hammock. But, a 2.5" TQ can not necessarily be directly compared to a 2.5" top loft(5" total) mummy bag in temp rating. It can be if the other variables are taken care of. Just something for a hammock noob to consider.
Similarly, when looking at an UQ and comparing sleeping bag loft/ temp ratings, loft is not the entire story. Fit is critical. Plus, any extra exposure to air flow- on the bottom compared to the top- might need to be considered.