Extending the range of your sleeping bag

i hate to say it again … but an en-rating is a very good reference point for the average person ..

as long as you have sufficient ground insulation … you should be able to handle the LL comfort rating if yr a healthy male who aint an old geezer … it aint perfect but its better than any marketing mumbo jumbo out there

the WM summerlite is rated as a 35F bag through testing … the MB is not rated at all

adding a down sweater and additional insulation for the legs and head will add around 10F for me ,,, depends on the sweater

10F seems like a good estimate based on my experience. After that, it's probably better to carry the next "step" up in a bag.

HJ

"10F seems like a good estimate based on my experience. After that, it's probably better to carry the next "step" up in a bag."

I don't think there's any limit like that

If I wear long sleeve shirt, down vest, jacket I can do 20 F

If it's colder, I need warmer stuff around camp before I go to bed, so no need to have a warmer bag

But if you look at Richard's graph of clo vs temp for different MET levels, the slope of the line for sleeping is steeper than the slope of the line for around camp MET level, so as it get's colder, there's a larger difference in clo between the around camp MET and the sleeping MET, so if you wanted to be perfectly efficient, you might want to get a heavier bag for colder temps.

Thanks for all the comments. They have really helped me in thinking this through. Here is where I am in my evolving thoughts on this subject.

When I used to backpack, back in the last century, I was a summer only camper, but temperatures would still dip down to freezing in the high mountains on occassion. I was perfectly warm in a not very good bag by the standards of the MB and WM bags that have been discussed here, but I slept in a small, double-walled tent where I'm sure it was somewhat warmer than the outside temperature and which would have blocked most of the wind. My intention now is to use some kind of a tarp tent, maybe a Hexamid, which will not create is own microclimate so much and in which I may be more exposed to the wind. In addition, I would like to extend my camping season into at spring and fall. I don't really know if I am a hot or a cold sleeper, but I strongly suspect that I am no better than average.

Based on the comments in this thread, the MB does not seem like the best choice if I want to be able to sleep comfortably in temperatures in the 20s. The MB is attractively priced and way light, but I'm thinking I need to bite the bullet and get a warmer bag, maybe a FF Merlin or Osprey. Those bags are 4-6 ounces heavier than the MB UL S DH 3, but my hope would be that by purchasing a warmer bag, I could avoid the cost and weight (9-10 ounces) of insulated pants. A bag like the FF Osprey is not a great bag for camping during some times of year in warm places I frequent like southern Utah, but it appears to have a full-length zipper, and I could thus use it as a quilt in warmer weather.

Thoughts?

i think you have it nailed …. a true en-rated sub 30F bag should be fine … if its too warm just open it up and use it like a blanket

"The MB is attractively priced and way light, but I'm thinking I need to bite the bullet and get a warmer bag, maybe a FF Merlin or Osprey."

Great minds think alike. I'm considering the FF bags too…. Sigh. This indecision is getting pricy.

I just used a Hexamid w/a MB UL Spiral #3 in very windy conditions (temps in 50s, low 40s). While warm, I wasn't exactly roasting. I'd imagine I'd be cold anywhere near the twenties or low thirties. Although I really do prefer to wear my puffy to sleep for the morning wake up temps, I like my tent airy but want to be "toasty" as well.

As Eric often suggests, I found haphazadly draping my puffy over me, in my bag, on those nights I couldn't decide if I was too warm or not warm enough worked really well too. Handy in the morning.

The hood on the MB bag is excellent though. I think I must be getting old, I was never concerned with being "toasty" before.

BTW the zipper wasn't where I felt a draft, it was in the back, along the seam where the front baffles meet the rear baffles. A friend of mine (a girl) sat outside with the MB (we were testing it, was only outside for 15 minutes) in her underwear in -2*C (very little wind) and said she felt the cold whenever she put her hand near the zipper. Although, to be fair, neither of us felt it was something we couldn't live with/sleep through.

"non insulated air pad"

Logan,
I think the non insulated air mattress made a big impact at reducing your warmth, like maybe 10 degrees.

Jeff

i've used a Ultra 20 with a UL parka, 200weight bottoms, bivy, medium weight wool socks, liner gloves, BPL torsolite pad down to -10C(15f) and was pretty toasty. but that being said, my warmest bag is a -18C degree bag and it gets to -30C here. so I must be a warm sleeper.

personally i would look at a summerlite for about the same weight but i believe has more down in it.

Not sure, as I've never used one, but I think using a bivy makes a marked difference. I still have my Golite Ultra 20, and am undecided as to what to do with it, but as much as I'd like, I don't think I could go down to freezing or below with a quilt given my sleeping style. Sigh.

"I think the non insulated air mattress made a big impact at reducing your warmth, like maybe 10 degrees." Yep! Already noted in my second post. But thank you for the guestimate on how big of an effect it had. Hopefully after I get my neoair I will have much better results.

^ the neo will be warmer, but w/ a r value of 2.5 your realistically looking at freezing as being the bottom (I've taken mine to 30 degrees several times and have been comfortable, but others haven't), of course a thin GG pad would fix that in a hurry

fwiw- if your looking for a 30 degree bag, also look at the Marmot Hydrogen- it's EN rated (males) at 29.8F and while I sleep a little on the warm end, I can attest that it's a true 30 degree bag

Went out this weekend with a Summerlite + Prolite 4 pad (full length). Predicted low = mid 20's F. I sleep a little cold. Normally, I'd expect to be pretty darn chilly in a Summerlite in mid 20's, but slept in a Patagonia down hoodie sweater and WM Flash down pants. Pretty toasty except for my feet, but no big deal. I think the hood on the down sweater makes a big difference. The sweater's hood nests inside the bags hood and makes it really cozy. Wore cap 3 base layers, 2 pr wool socks, light weight fleece cap, light to mid weight fleece mittens.

HJ

^ down booties and you would have been in business :)

I might try that although there's a limit as to what I can squeeze into a Summerlite.

HJ

I've worn goosefeet down booties in my Summerlite without feeling cramped. The funny thing is, if my feet are seriously chilled when I go to bed they just don't warm up in the booties. If my feet start out warm I find the booties too hot in the bag; I just wear a pair of heavy wool socks. Coldest I've slept this way is around 20F (outside), in a small 2-person 3-season tent with one other person. It may be relevant that I have circulation issues in my extremities when it's cold.

Is it possible that by wearing two pairs of socks you're restricting blood flow to your feet?

yes if its tight … same as boots that are too tight …

always arm up the bag and clothes before sleeping … which usually means doing situps inside until warm …

Richard, I apologize if I am repeating something here. I actually received the same advice from this forum about 2 years ago. I exchanged my Northface Blue Kazoo 20 deg bag (50 oz) with a Mountain Hardware Phantom 32 (23 oz.) I then replaced two layering items, a 12 oz fleece longsleeve and a 10 oz pair of long underware with Montbell Down Inner pants and parka at 8 oz and 9.5 oz respectively. I also added Goosefeet down socks at 2.1oz. Overall I saved myself 29.4 oz. (Almost 2lbs:)

The lowest temperature I have camped in with this setup is 25 degF an I was really toasty. (I sleep on a Thermarest Prolite Plus in a Big Agnes SL1.)

Larry

I think the main issue in this case was the size of the bivy I was in. The bivy is too tight with a 1.5" thick pad. My foot area felt kind of cramped, and I definitely had some down compression going on, particularly over my arm/shoulder (I'm a side sleeper). Still, even with some compression, I was plenty warm. Insulation success; bivy fail.

HJ

Digging this out as the topic fits:

I wonder: If I use a down sleeping bag rated -20C with only base layers on.
Then use e.g. a down jacket with 200g of down – how far can I decrease the sleeping bag rating?
(I’m aware that legs will be colder)

Christoph, there’s a formula somewhere (here, I think) for layering two bags. And there’s a table for easier use here: https://support.enlightenedequipment.com/hc/en-us/articles/115002770588-Layering-Sleep-Systems

Not sure how to translate that into bags/quilts and jackets.

But since I have an inkling of where you intend to use your system, I’d advise caution. I find a lot of people who proclaim that a bag keeps them toasty at the advertised (EN limit) temperature are already wearing quite a lot – or at least have those warm clothes at their disposal for emergencies. It’s actually quite amusing when you read the review threads on manufacturers’ sites: “Works as claimed! I was toasty down to the rating of this bag wearing nothing but a down jacket, down pants, moonboots and a centrally heated house around me.”

Methinks it’s the kind of thing that calls for prior experiments in the garden.

I use a +20°F quilt down to about -5°F while wearing down parka and down pants, also while using an Xtherm Max with a 5/8″ CCF pad on top of it.

But that’s me.

+1000 to “experiments in the garden”……..  for such conditions I would never take the word of anyone, nor believe any chart, that says this or that will work. There’s no substitute for personally testing in actual conditions.

Thanks for the answer guys!
I’ve already got experience in the Alps, however, the reason I’m asking is that I’m using 2 layered sleeping bags at the moment. And I want to replace them with a warmer, single sleeping bag.

Right now I only sleep in the base layers. But as I’m also looking for a new down jacket, I wondered how it would affect my sleeping bag rating – since I’m carrying the jacket anyway, I might as well wear it in the bag.

Yeah, but it’s not just about the Alps, Christoph.

I’m aware of the fact that you probably have more experience there than the vast majority of us.

It’s more about you, a bag you don’t yet know and a jacket you don’t yet know.

Kinda risky to bank on anything working as you’d want it to.

Ah – yes sure, I usually try my combinations gradually increasing the altitude (and lower the temperature). I don’t trust any new ideas as I usually change my mind a few times :)

Why not just purchase the jacket first?

Presumably, you’ll want a jacket to meet certain daytime conditions… which you could then try with your existing bags to roughly assess what it can do during the night.