Winter weight down clothing instead of sleeping bag for summer adventures?

Worth looking at. I think the clothing is going to be less efficient than the same weight's worth of down bag because your arms and legs are isolated. Even if you had the same loft in the clothes that you did in the bag I think it would be less efficient. Still worth trying though. If it won't work to freezing maybe it will work to 40, who knows. I'd say try it in a low risk situation and tell us what happens. One advantage is that if you get a bit chilled you can get up in your clothes and walk around a bit than lay back down once you've generated some heat. You can't do that when you have a warm quilt but a skimpy jacket.

In the summer I don't see temps below freezing normally, even in the alpine of Colorado. So I would never be carrying a down parka of that weight (17oz parka) in the summer so definitely not multi-use gear to bring that along. A typical summer setup for me would be my 15oz 40 degree Katabatic Gear Chisos quilt and my Patagonia down sweater (vest if temps above 40). Where I think you really save weight is in the shoulder seasons where you can take a 40 degree bag down into the 20's with a warm jacket that you will need in the morning/evenings anyway.

@Luke: That's true about the lack of efficiency. I didn't really think about that. Would that fact be canceled out or lessened by the smaller volume of air required to be warmed? I'll have to test it out when it finally warms up here—July? :[

@Randy: You're making my point exactly though. A Chisos is 15oz and your down sweater is 12oz, for a total of 27oz. That's 1oz lighter than the system you're naysaying but only has 10oz of down (versus the 13oz of the parka/pants/booty combination) and is made up of less useful items for extending your trips into true spring/fall/winter conditions.

it isnt "weight efficient" … but if you have sufficient down, it doesnt matter …. you might be a tad warm in camp, but jut unzip then …

the danger is if yr down gets wet … yr screewed with no backup … thats the risk you take

some alpinist dont bother with bags anymore in light and fast ascents … they just bring a big belay parka and pants … but then they arent exactly setting up a proper camp either …

Maybe you have your math down, but I have always assumed that bringing extra clothing for sleeping is far heavier than bringing a warmer bag.
I bet if you added up all the weight of down clothing that would keep you warm down to 30 degrees, a 30 degree bag would be lighter.
For examples, on your legs a bag or blanket is warmer than pants for the same reason that mittens are warmer than finger gloves. Your legs are separated. You also have down on both sides of your leg (left and right), instead of a bag. Same with your arms.

I would only really consider this kind of setup in the far north like Alaska where the weather can turn nasty and the temps can drop low, but because of the long days the temperature difference between night and day is minimal or non existent.

In your example, the FF Helios is 53% down (by weight), the down pants are 31% and the booties are 50%, for an overall percentage of 48% (13oz/27oz).

I believe the main reason this isn't commonly employed is because sleeping bags are typically more weight efficient than down clothing – meaning they have the highest proportion of their weight in down. For example, Zpacks 20 degree sleeping bags are 65% down, so you could get the same 13oz of down for 20oz total instead of 27oz.

Now opting for only this sleeping bag wouldn't be a very versatile tactic, since you'd have no insulation for when you're outside of the bag. Accordingly, my strategy is to employ just enough down clothing to comfortably meet my needs around camp, and then put everything else in the sleeping bag. So if I wanted 13oz of down total, I might opt for an 18oz Zpacks bag with 11oz of down, and then a 4oz Black Rock down vest with the last 2oz of down. That sums to 22oz instead of 20oz for the same total amount of down, but it's more versatile. If 13oz of down is going to be enough for sleeping, 2oz on my torso is probably enough for around camp.

Ideally I'd like 3-4oz of down in clothing and another 9-10oz in the bag probably. If you found an 8oz down jacket that was 40-50% down and then got a sleeping bag at 60% efficiency, then you'd wind up around 24-25oz and have a well rounded system. It would probably actually be better than the all clothing system, because a Helios parka with 9oz of down is down is darn warm for wearing around camp in 30-40F temps. I say 30-40F temps, because it seems like we're expecting a nighttime low around 20F if we're only packing 13oz of down total.

Taking this further, going to all clothes and no bag is likely to be the heavier still to get the same amount of down. It is true that some super puffy parka's have pretty high % of down like your Helios, but you're probably not going to get as high as sleeping bags do. If you have really weight efficient down layers like the Helios, then you've got more flexibility between taking more layers and a less warm bag or vice versa, but for more people this is a considerably heavier option.

As I hiked 1500 miles on the AT last year… there were definitely thoughts of shedding the sleeping bag, and keeping a few things to carry over from winter. Here are the 2 bags I own. I was going to just take the 2 jackets and pants, but ended up with the parka and the sleeping bag. I believe it was a good choice.

WM Ultralite
MontBell SS#3

MontBell Alpine Light jacked Medium
MontBell UL Down Parka Small
MontBell UL Down Pants Small

I really, REALLY wanted to get rid of my WM sleeping bag and just roll with the MontBell jackets and pants setup… but I realized a few things personally.

You cannot bring a bottle of water into your sleeping bag and "Warm Up" if you don't have a bag to warm. I have used hot bottled water to help soothe cold temperatures. No bag, and no option. I have tried to compare these multiple items to a sleeping bag in volume and packability. The sleeping bag allows me to have a very small hole to breath from. Maybe I sleep cold, but I just like being bundled up myself.

It LOOKS as though it would be less weight-efficient, but that could be deceptive. If you carry a good set of down clothing for the evenings plus a down bag for the night, that is likely to be heavier than just the down clothing.

Can I suggest a very light bivy bag to shed any wind and keep frost off your down clothing though?

cheers

If you have enough down clothing to keep you warm in the coldest part of the night, you are probably carrying too much clothing.

Just the right amount of winter camp clothing can extend the warmth enough that you could get by with a light three season bag/quilt, except in very cold environments.

If you own the stuff and are comfortable, what the heck. It's easy enough to do the math on the weight. It's another twist on using your quilt for camp clothing a la Jack's R Better serape-style quilts. My first impression when reading your post was to just add a light breathable bivy sack— you will be hosed if you get the down wet. You can always do a test drive in the back yard to gauge the warmth and condensation.

Another take for summer stuff is to split the difference with a light bag/quilt and light insulation. I got a Therm-a-Rest Tech blanket super cheap to use as a hammock top quilt or uber-minimal ground quilt, supplemented with the insulation layers I would be taking anyway. If I'm cold in camp, I could always throw on the blanket. I'm talking summer nights in the 50F or higher range and using mid-layers like Power Stretch or R1 with windshirt, light hat and gloves and maybe a puffy vest.

It always adds up to use the lightest bag possible, assuming you are wearing all the clothing that you already have in your kit to extend the range. It is just simple multiple use. Some folk even wear their rain gear. I would if I found things unexpectedly cold, but not as a habit.

Last November and December I did several trips with a Tim Marshall Cuben Tarp down to 28 F. Hard to beat an 11 oz quilt. I am a cold sleeper and that night at 28 was cold for me until I put on my sub 4 oz Montbell UL vest. I was also wearing a Mountain Hard Wear Cliffer LS T (merino wool/poly), which doubled as my hiking shirt, and Cap 1 bottoms. All the other nights were below 40 F.