As an ultralight backpacker, I'm always intrigued by multi-use gear. It should come as no surprise, then, when I fell in love with the wearable quilts. Wearable quilts are designed to function as a normal top quilt or sleeping bag, but have openings for arms, legs, and head to allow the insulation to be worn.
One such quilt that I have is from Jacks "R" Better, specifically the Sierra Sniveller. The Sniveller series quilts are truly multi-use and can be used as top quilts, under quilts, and jackets (or, more accurately, a "serape").
(This image is _horribly_ blurry, but it's the only one I could find for now that shows me wearing the Sniveller in the field).
Another wearable bag I have is the Exped Dreamwalker 650. This is a traditional sleeping bag with zippered arm holes and an open foot area that can be drawn up to convert the bag into a full-length parka with a hood.
A typical backpacking kit in the fall/winter includes a puffy jacket (typically down) _and_ a sleeping bag/quilt. On a recent backpacking trip, I decided to leave the jacket at home and rely solely my quilt for my "around camp" formal wear. Our camp was at 9,500 ft (2,900 m) and it dipped down into the low 40s °F (4 °C) by 10 PM. Wearing the Sniveller while walking around camp was great. Not only was I toasty warm around my torso and arms (just like I would with a puffy jacket), but I had extra coverage over my buttocks and upper legs. It was wonderful.
Getting up in the morning when it was in the upper 30s °F (3 °C) was no problem. I just ducked my head into the bag and popped open the head slit, which enabled me to keep my warmth around me. Bathroom breaks are easy and I don't have to worry about losing my warmth.
Ditching my down jacket saved me more than 16 oz. (454 g.)!
Here is a comparison showing a jacket and quilt combo stacked against wearable quilts/bags. High-end down-filled 3-season jackets typically range in weight from 12 to 16 oz. (340 to 454 g.). Most retail down-filled jackets are heavier.
WEIGHT SAVINGS BY USING WEARABLE QUILTS
Compared to 12 oz. jacket + 19 oz. top quilt (31 oz.)
Exped 650: -7 oz.
Exped 450: none
Sierra Sniveller: 8 oz.
Compared to 16 oz. jacket + 19 oz. top quilt (35 oz.)
Exped 650: -3 oz.
Exped 450: 4 oz.
Sierra Sniveller: 12 oz.
Compared to 16 oz. jacket + 22 oz. top quilt (38 oz.)
Exped 650: none
Exped 450: 7 oz.
Sierra Sniveller: 15 oz.
In my own experience with wearable quilts, the comparison isn't exact. Wearable quilts arguably provide more coverage and offer more warmth compared with jackets. However, jackets provide more mobility in some cases and may be desirable in some circumstances. Your mileage may vary.
An under quilt can easily be converted into a wrap (e.g., sarong) around the legs, a throw around the shoulders, or a blanket to make it pull double-duty.
For me, I think the case is closed. Even with the heavier Exped bag, I am gaining a much warmer and roomier jacket with much more coverage. Depending on how I pack, the weight is a wash, or I could save more weight by eliminating an under quilt (the Exped can be used as an over bag or "PeaPod"), but I'm still getting more wearable gear in the deal. With other quilt options, like the Jacks "R" Better Sniveller series, I can get a significant weight savings and have a roomer, warmer jacket for around camp.
Exped Dreamwalker 650 (20°F 800+ fp) WEARABLE: 38 oz. (1 kg.)
Exped Dreamwalker 450 (30°F 750+ fp) WEARABLE: 31 oz. (850 g.)
Sierra Sniveller (20°F 800+ fp) WEARABLE: 23 oz. (652 g.)
Nunatak Arc Alpinist (20°F 800+ fp): 22 oz. (624 g.)
Burrow 20° Quilt (20°F 900 fp): 21 oz. (595 g.)
Mamba 3-season regular (20°F 850 fp): 19 oz. (539 g.)
High-end Down Jacket (800+ fp): 12-16 oz.