If all you do when you make a quilt is basically leave off the zipper then sure, it will only weight a few ozs less than the bag.

If you want to make a real comparison you need to weigh a bag that works for you at the lowest temp you want and then weigh a quilt that works for you at the same temp. This is a real involved and expensive process, but gives an accurate comparison. If your quilt ends up being that same size as the bag, well then it's not going to weight much less. However, if it ends up being smaller then it will.

Personally, I think the real advantage of a quilt is that it a much more comfortable sleep with no weight penalty. It takes all that useless insulation and puts it somewhere I can use it, namely to spread out!

As always, everyone is different. Quilts work better for some, bags for others.

I don't think they're fudging the weight numbers, I just don't think the bag is going to be as warm as the quilt.

As Lawson said:
6' of #5 zipper tape and 1 #5 locking slider weigh 1.5oz...

Check the site and you'll see they're only adding 1oz of fill to the bag, but the bag is only 2oz heavier. SO, 1.5oz of zipper plus 1oz of fill does not equal 2oz. There's compromise happening somewhere. Not to mention, since they put the zipper on the top, most of the fill is now underneath you (unlike a traditional bag where at least 50% of the fill is on top and sides).

I'm very skeptical this bag is as warm as it's "equivalent" quilt.

id say that qualifies as fudging the temp numbers ;)

id love to hear from someone who uses that bag ...

I'm a side sleeper and I tried a prototype quilt for a bit but quickly realized that draftiness was a problem that I didn't want to have to deal with when temps really started to plummet.

The perfect compromise for me is a zipperless, slim cut mummy that opens up wide at the top to accommodate wearing a jacket and other layers to bed. Doesn't feel constricting, and you can turn with the bag.

For example, the Feathered Friends Vireo. Weighs 16oz With a light insulating jacket and is conservatively rated to 25 in the feet, 45 in the torso. Combine that light jacket with a beanie and you're sitting pretty at around freezing temps. For 16oz.

Joe at Zpacks has made hoodless bags at incredibly light weights.

I like quilts because I can control the width. In warm weather, it's easy to vent, twist, turn, or cinch it up in the middle of the night. In cold weather, I put on a puffy jacket, widening up my quilt, but I'm still protected from drafts.

I tried quilts for a period of time, and went back to a WM Summerlite as my main sleeping piece. I sleep on my side most of the time, and turn quite frequently - the drafts I got with a quilt lead to a few cold nights. To properly eliminate them, I would need a quilt almost as wide as the girth of my Summerlite, which negates most of the weight savings. I also felt the hood on my bag helped keep warmth in a lot better. Just my experience...

Aaron - curious to know - were you using any sort of strap or tie-down system to keep the quilt sealed down? Or were you letting gravity do the work?

What's the big disadvantage with the Big Agnes style bags where there is no insulation on the bottom, but there is a sleeping pad sleeve instead? Seems like it solves the problem of compressed down on the bottom of regular sleeping bags and the problem of drafts in quilts.

Also, another same manufacturer quilt/sleeping bag comparison would be the GoLite 3 season (20 degree). The sleeping bag is 1 lb, 14 oz and the quilt is 1 lb 7 oz....or a 7 oz difference in the regular size.

The issue with BA bags is for side or stomach sleepers. You roll but your face gets buried in the hood.

I loved my BA bag, until I switched to a quilt. But, I don't use the hood. However, the few times I have slept when it was cold enough to use a hood I stayed on my back for some odd reason.

A pad sleeve spoils the variable girth feature that's so important to make quilts versatile. It makes the bag somewhat rigid, it doesn't drape well around the body; you don't need insulation under the contact points but you do around them.