If you were to get one of the polar/everest suits like this one, would you need a sleeping bag? This weighs 3lbs 15oz, comparable to a really lightweight 15 degree bag or so, and I bet this would keep you much warmer, plus it serves as your jacket and pants!

http://www.mountainhardwear.com/Product.aspx?top=1426&prod=1311&cat=1463&viewAll=False

I've experimented with components other than a sleeping bag and concluded that the sleeping bag is the most efficient per pound, other things being equal.

For example I tried a puffy Eddie Bauer parka with a half bag. I was colder in this combo, much colder, than I would have been in a full size bag that weighed less than the combo.

The dual use of the clothing/sleeping bag combo looks like it might save some weight but I wouldn't want to risk it. If the outfit got wet from sweat or rain I'd be without a bag for the night.

Don't do it! Or find a time and place to experiment (such as car camping)and try both methods in the same environment. A sleeping bag provides loft, which is the critical issue. I have left the sleeping bag at home and tried various clothing substitutes...and been miserable even in mild climates. Perhaps a down suit would come closest to doing the job.

This idea gets brought up on various boards every winter. It is a bad idea. First of all, for $900 (the cost of the MH suit) or maybe a bit more, you can buy the best -40C sleeping bag on the planet such as the Western Mountaineering Bison. If you need a -40C bag, buy one.

Second, a suit will not keep you as warm as a bag designed to be used at the same temperature. Separating your limbs eliminates the advantage of your body working as a unit to keep one space warm rather than five separate ones. I'm sure other people will have better scientific explanations than I am offering, but the principle is the same reason why mittens are warmer than gloves. If it was a good idea, high altitude mountaineers would do it, and they don't.

Third, the MH suit is not designed to be worn in warm weather; it is intended to be worn in extremely cold weather at high altitude. You would be swimming in your own sweat in this thing at anything near 15F if you tried to do anything in it other than maybe just sitting still. Will it keep you warmer than a 15F bag? Yes, but it would be useless for any other purpose at those temperatures and you have little or no way to control your venting of the heat you would be generating as you walk around in it.

If you want to see what Canadian winter campers who are out in -20C or colder weather wear, visit www.wintertrekking.com. None of them are wearing anything like this and none are using it for a sleeping bag substitute.

What leads you to believe that? The suit has much more surface area to lose heat than a bag.

All other things being equal e.g. the weight and fill power of the down I would always choose a bag over a suit if keeping warm was my main concern.

Mittens are warmer than gloves (all other things being equal), I look at sleeping bag vs down suit as kinda the same thing on a larger scale...

However, wearing insulated clothing inside of a sleeping bag does extend its range some.

I look at sleeping bags as the generic way to sleep warmly at night. But when looking at modifications and/or alternatives, specific applications for individual situations come in to play with increasing importance.

For the last several years I've not taken a sleeping bag on the trail relying instead upon cold weather clothing. This gave me a significant savings in weight and bulk and worked well for me to the low-20s in a hammock. Presumably it'd be warmer on the ground but I've not been 'on the ground' in those temps with this system. The temp limiting factor, FYI, is the thin pad I use in the hammock although the clothing should be good for much colder temps. This isn't a revolutionary practice...it's simply getting dual use from the cold weather clothing and reaping the weight savings.

I firmly believe this system works for me because of the area and conditions where I backpack. From May thru October, I can find freezing temps any night...hard freezes in the early and late part of that season. However, most of the daytime temps range from cool to hot. I gotta carry the cold weather clothing but I virtually never wear it when hoofin' down the trail. But it makes for a fine sleep system during the cool/cold, low humidity nights of my home range.

There are some very important considerations and qualifications, though. First, I have the luxury of timing my backpacks with weather forecasts. I can easly postpone/reschedule trips which greatly reduces my chance of being caught in unexpectedly harsh conditions. Second, the further from the trail head I get...the longer the time it takes to bail-out to safety...the more I rely on more traditional systems.

My point is that with some thinking and planning one can move far away from the traditional sleeping bag and still be comfortable and safe. But the two biggies of safety and comfort become more dependent on the conditions to be faced when one doesn't carry a broad range sleeping bag. In this sense, moving away from a traditional sleeping bag merely involves 'fine tuning' of the sleep system. IMO.

FB

My approach is the reverse of what you are suggesting and what Fiddleback is recommending. I wrap up in my sleeping gear to stay warm before bedtime.

For three season conditions, I seldom need more than a light insulating layer when I am hiking; my activity keeps me warm enough that usually a wind-shirt over my base layer is all that is needed.

I do use insulated garments in camp, morning and evening. But, rather than carry an insulated jacket, I simply wrap my sleeping bag or quilt around me. In fact, my quilt has a head hole that allows me to wear it as an insulated poncho. So, rather than sleep in my clothes, I wear my sleeping insulation to stay warm before bedtime. My sleeping bag weighs about 1.75 lb, my quilt weighs about 1.2 lb. I doubt that I could carry a down jacket and pants (or short sleeping bag) for any less weight. Wrapping up in your sleeping gear is probably not as efficient for staying warm as wearing insulated clothing. On the other hand, I suspect that sleeping in clothing is not as efficient for staying warm as using sleeping gear.

My 15* bag weighs in at 2lbs 2oz... a full 1lb13oz lighter than this suit.

Huh? Western Mountaineering's Versalite 10 degree bag is 2lb even and their 20 degree Ultralite is 1 lb 13oz.

I have Feathered Freinds Rock Wren with zippered slits for armholes and an openable footbox. That's nice to get up in the morning and not get out of the sleeping bag. If I was going more in that direction and had unlimited funds, I'd seriously look at Nunatak's Raku 20F with sleeves in Quantum fabric at 1 lb. 14oz. and Epic shell at only 35oz.

I've tried it, with two solid down jackets on, one with down hood.

Went out in nearby backcountry at about 35 deg. and moist.
I froze and barely got a little sleep from being cold. I even tried a space blanket on top --- instant drip.

What I do instead which does work is to use my bag as a quilt or down jacket. My 3 season is a feathered friends winter wren, but any bag can work..

I think that I will continue to carry my trusty old sleeping bag...sabre11004...

The first step that you take will be one of those that get you there !!!!

For a number of years now, I have been using the Feathered Friends Vireo (half bag) with the FF Volant (down jacket & hood).
http://www.featheredfriends.com/Picasso/Bags/Specialty.html

I have done just fine with this combo in below freezing temps.

If I had a full length sleeping bag, my down jacket would have just added 1.5lbs to my pack weight. Then used as a pillow. Who carries a 1.5lb pillow?

The Volant sure looks like a nice jacket. If you owned (or wanted) one, this would certainly be one workable option.

However for someone looking for the lightest and most versatile option, there may be other configurations. For example, the Vireo plus the Volant are at least 38oz (FF doesn't give a weight for the hooded version) and a Western Mountaineering Ultralight plus their hooded Flash jacket is also 38 oz. and you have both a jacket and a bag which can be used together to extend the range of the bag by probably 8-10 degrees down to 12 or 10F.

The Nunatak Raku is an even lighter option http://www.nunatakusa.com/site07/other_bags/raku.htm

I have an old Gerry elephants foot. I've never used it. Maybe I'll give it a try to see what it's like.

I see a sleeping bag as a safety net if your clothes should become unusable for some reason. If you fall in a creek, assuming you keep your bag in a mostly waterproof sack, you have a refuge. If you're wearing your sleeping when you fall in the creek you're in trouble.

I do not think this is a good solution for everyone. The weight you cite is NOT light! That said, my partner uses a simlar system and is very happy with it. He has an 800-down expedition parka and had an elephant's foot made specifically to fit him by Feathered Friends (Seattle manufacuter). He is a claustrauphobic thrasher when he sleeps. Now he sleeps better. Also we are climbers. The parka is taken on climbs as emegency gear. We have been caught on a climb before and had to bivouac. And he gets to get "out of bed" and keep on a plush parka in the mornings! The total weight of his system is the same as my 10-degree sleeping bag 2# 14 oz. But for most backpacking purposes, I do not think it is the best solution and it is expensive too.