Looking for some advice.
Very experienced lightweight backpacker, mostly in the rockies.
One piece of gear that I have resisted changing out was a cold-weather bag. Have a WM Highlite for the high summer/lower elevations...

But this year I will be around treeline in CO in early september. Certainly a chance of some snow, and a night down around 20 would be a real possibility.
Basically, I am trying to decide on a new bag, going as light as possible...but I want to be warm.

So...20 degree bag, 15 degree or 10 degree? Budget not the concern - weight and comfort are.

Will be paired with a thermarest xtherm which has a 5.7 r-value.

If it matters, I am in a Stephenson 2R. Because I like condensation.

Thoughts?

My bag is a Western Mountaineering Ultralight, which the manufacturer says is a 20*F bag. Its actual EN13537 ratings (found on EU websites, since WM doesn't reveal the info) are comfort, 24*F and lower limit, 17*F. I have taken the bag down to 15*F comfortably by wearing all my insulating clothing inside the bag, over a vapor barrier suit, with an R5 pad. and with a 75 lb. dog curled up against me. That's effectively 10*F lower than the bag's comfort rating. Any colder, and I would have wanted at least one more dog!

A lot depends on whether you're a warm or cold sleeper, whether you can use a vapor barrier and how much insulating clothing you're willing to carry. There can be nights when it gets down to 10*F or colder at higher altitudes that time of year, especially if you're camped down in a low-lying area (remember, cold air sinks).

Remember, those EN13537 ratings are more accurate than those dreamed up by manufacturers' marketing departments!

I second the comment on it depending on whether you sleep warm or cold. I typically like temps a few degrees colder than most people, personally, so I'm more likely to push the lower limits of a bag.

That said, my quilt (Enlightened Equipment; they no longer sell the style that I own but it was just their basic quilt at the time) is rated to 10 degrees and hasn't been used in anything colder than 40, because I bought it with the intention of winter camping and haven't been out in cold weather since.



Are you looking at down or synthetic? I went with down because I prioritized light weight and compressibility (weighs about 2 lbs, packs down into a 6L-2L compression stuff sack), and I absolutely love it except I'm paranoid about it getting wet.

As mentioned, sleep layers. If you aren't planning on further extending your seasons, a true 15 degree bag or quilt should be plenty. I use an EMS Mountain Light 15 down to 0 F by wearing my down puffy and a hat. Considering the morning is going to be cold when you arise, and temps will drop in the evening, you may consider factoring in your cold weather gear as sleepwear. You'll need it, might as well use it.

OM,

I'm glad you mentioned it being colder at lower altitude. That has been my experience in Colorado but I didn't want to say anything. The coldest sleeping seems to be around 9,000 feet here.

SNS,

Since you are comfortable in Colorado with a WM 40 degree bag, I would think you could do well with a WM 20 degree bag, but don't take my advice. There are many WM dealers in Colorado. You can find phone numbers on the WM site. I suggest giving them a call.

The owner of Mountain Chalet in Colorado Springs has done lots of backpacking and, if he has time, is willing to share info.

I mainly camp and hike in the Utah Rockies. I bring a 20F quilt for late spring to early fall. There isn't much difference between a 20 and 15 F bag.

Thanks for the advice - will ask at the Chalet next time I am in there.
(Went to CC; been going to the Chalet since the late 80s.)

The warm vs cold sleeper thing is a good point...a data point I should have mentioned.

So, a night that dips down to 20 degrees, with two layers of thermal tops and bottoms, a fleece hat and wool socks, in a WM Highlite (supposedly a 35 degree bag) I am wishing for a dog or two...

If you remember Three Dog Night, in actual life that's a cold enough night that a shepherd would need to curl up with three dogs to keep warm!

Some like deliberately to use a less warm sleeping bag and regularly use insulating clothing for cold temperatures. I like to have my sleeping bag warm enough for normal conditions, and my insulating clothing as a reserve for when its's unusually cold at night. As suggested in my above post, occasionally I've needed that extra margin of warmth!

Re: Synth. vs Down:
I have always used down and have learned how to deal.

That said, there are some interesting water-repellant down products out there these days...

I've had a three dog night or two, but that when when I was younger and stupiderer.