Simple Math Question

[lwhikerchris]

Approx. how many extra degrees of warmth could be had by combining a 20° down sleeping bag on the inside of a 40° synthetic (climashield apex insulation) bag?

[nsherry61]

Probably not as much as you would like since one bag inside another tends to compress the insulation on the inner bag quite a bit.

If you drape the synthetic bag open and over the down bag you will probably get the best insulation. I drape an unrated quilt (probably about 45 degree) over my 20 degree bag and stay warm down to about 0 degrees, but your mileage will probably vary a great deal. Best thing to do it try it out and see in your back yard or a local park, somewhere near your home or car so you can escape if things get too cold. Also, don't forget to upgrade your pad underneath you since that plays a much bigger role in warmth than most people realize.

[lwhikerchris]

Thanks for the reply nsherry. Underneath I have a Thermarest xtherm.

[John B]

Probably not as much as you would like since one bag inside another tends to compress the insulation on the inner bag quite a bit....


This is an absolutely vital point to keep in mind, and not only for trying to put one bag inside another, but even for sleeping bag girth in general.

I am 6'0 and have broad shoulders. I bought an expensive Western Mountaineering bag with a 20 degree rating. Used it on a late fall hike and nearly froze. It didn't occur to me until afterward that my shoulder girth was really compressing the down, thus substantially reducing the temperature rating. To me, the simple test is if you can wiggle around a bit and turn side to side while inside the fully zipped bag, you're probably ok. But if you turn side to side and the bag kinda turns with you, then the bag girth probably isn't sufficient.

That's my .02

[Cheyou]

http://www.enlightenedequipment.com/blog/quilts-106-quilt-layering-for-cold-temps/

[George]

if everything worked together perfectly, and the ratings were realistic than in theory the rating would be around zero

[colorado_rob]

http://www.enlightenedequipment.com/blog/quilts-106-quilt-layering-for-cold-temps/Fantastic to see this quantified by a reliable source. thanks!
..
I think the argument against stacking bag/quits/etc because of compressing the down is overblown, and I know from experience combining bags works great. Down bags aren't perfect anyway because of the way down shifts around in the baffles. Combining bags tends to "smooth" this out a bit and eliminates any thin-down cold spots. the loss of warmth due to a little bit of over-compression is there, but a second order effect.
..
Thanks again for that link. In the past I estimated by looking at spec sheets for temperature rating vs. total loft, like on the WM sleeping bag spec sheet, like this one:
..
http://www.westernmountaineering.com/product-details/sleeping-bags-specification-chart/
..
For example, take the everlite 45 deg at 3" of loft and combine with the 35 degree Highlite at 3.5" loft. Put them together and if everything were perfect, that's 6.5" of loft, except maybe you'll get 5.5 or 6", which is the same as about a 15-20 degree bag. Because the combination eliminates "cold spots" (when the down insulation "leaks" because of voids), I'd go on the more optimistic 15 degree rating. The chart in the link seems pretty close to this (15 degree) if you interpolate.

[Studlintsean]

Simple Math? Is this one of those common core equations people have been complaining about?

[squeezebox]

Common sense and simple math don't always add up.

[rafe]

It's all about the loft you achieve when the two bags are combined. Search around on the web and you will find charts that give temperature rating based on the loft (measured in inches, typically.)

I've done this numerous times with no major issues or surprises.

[MuddyWaters]

Ive done it with no issues.
Its harder with quilts because not sealed up.
I wouldnt hesitate to use my 40f quilt inside my 28F megalite, well into single digits. I expect feet might be a tad cool, but thats all. When ive tried this out at normal temps , too hot to stay inside immediately.

[Feral Bill]

If the outer bag is reasonably large, you shouldn't lose too much loft.

[4eyedbuzzard]

From a purely scientific standpoint, the math, or more accurately the physics, isn't as simple as it might appear. There are a lot of variables involved in how heat transfer occurs through an insulation system. The article and chart Cheyou linked to from EE demonstrates that it's not a simple addition situation.

In terms of real world practicality, as colorado_rob and rafe have mentioned, the overall insulation loft achieved will likely provide the best estimate of performance. One thing to keep in mind is that the inside girth of the outer bag should be as large or slightly larger than the outside girth (inside girth + loft) of the inner bag to prevent compression of the inner bag's insulation, which would restrict total loft. Note that mummy bags are cut differently in terms of girth at various points - there is no standard as to how girth at shoulder, hip, foot box area relate, especially between different manufacturers and models. Again, real world and not in sub-zero conditions, the outside bag needs to be somewhat larger than the inside bag to allow it to loft.

[Venchka]

Over bags have been around since forever. Quilts are the new overbags. Quilt over sleeping bag. Take advantage of the sleeping bag's hood, collar, etc. to hold in your body heat. The EE chart has appeared in numerous threads. Good confirmation that the ancient ways worked without benefit of the interweb.

Wayne

Sent from my AT100 using Tapatalk

[The Cleaner]

Back in the early 80s when down bags were really expensive,I purchased a Wilderness Experience 10* Polarguard bag.It weighed about 4.5 lbs.I added an Early Winters gore tex bivy and used that for many years to temps at 0* and below.Temp ratings aren't worth much when it's cold and windy and you're in a windy shelter or a UL single wall tent that requires "ventilation" to prevent condensation.Buy a good bag and a good bivy or tent.Right now there are several hikers in Hot Springs waiting on the weather to get better.Windchill in the area for tomorrow night is -10* to -20*:(

[lwhikerchris]

Thanks to everyone who replied to my question. The information, links, and charts are very helpful. I actually tested my 20°/40° quilt setup last night for a while in 12° temps here in Pennsylvania and was pleasantly surprised by the level of warmth the 2 bag combo achieved. I'm going to try it again tonight since it's supposed to go down to 1°F.

I need to figure out a solution for my mouth, nose, and eye area since the air was pretty cold. Right now I'm using a fleece balaclava and Black Rock down hat.

[Mags]

Shawn forry and Justin lichter used the same system on their PCT thru hike last winter. A synthetic 40f quilt was used over a 20F down quilt, the synthetic quilt protected the down quilt and absorbed most of the moisture. Simple and effective.

[Gambit McCrae]

My buddy and I tented right ontop of the apex of Chestnut Ridge in tarptents ont he first freeze of the year, it was down in the 20s. he used 2 montbell 45* bags and was warmer then I was in my 15* bag

[rafe]

Here's a chart that gives temperature rating as a function of loft (inches)

http://www.zpacks.com/quilts/down_loft.shtml

[George]

I need to figure out a solution for my mouth, nose, and eye area since the air was pretty cold. Right now I'm using a fleece balaclava and Black Rock down hat.
http://www.amazon.com/Ergodyne-N-Ferno-6970-Extreme-Balaclava/dp/B0091CC38A/ref=br_lf_m_5pjutkm62amr8k3_ttl?ie=UTF8&s=hi

breathing through a copper coil is about as good as it gets for below zero

[Puddlefish]

http://www.amazon.com/Ergodyne-N-Ferno-6970-Extreme-Balaclava/dp/B0091CC38A/ref=br_lf_m_5pjutkm62amr8k3_ttl?ie=UTF8&s=hi

breathing through a copper coil is about as good as it gets for below zero

There's no way I'd be able to resist talking like Vader in that, people would hate me... more.

[squeezebox]

http://www.amazon.com/Ergodyne-N-Ferno-6970-Extreme-Balaclava/dp/B0091CC38A/ref=br_lf_m_5pjutkm62amr8k3_ttl?ie=UTF8&s=hi

breathing through a copper coil is about as good as it gets for below zero
what kind of Ninja sword comes with it?

[nsherry61]

. . . I need to figure out a solution for my mouth, nose, and eye area since the air was pretty cold. Right now I'm using a fleece balaclava and Black Rock down hat.
When it gets down below 0 (so sleeping outside of a tent typically), I frequently put a layer over my face, generally either a fleece neck gator, or more frequently my merino wool buff, either of which let air flow through them pretty easily and can be rotated around to the side of your head/neck if they get wet and need to dry out/thaw out, giving you a new dry place to breath through. Above 0 degrees, I find that as long as I'm not gasping for air, I can breath carefully and do just fine without having to breath through something. Also, if your face is surrounded in a bit of an air pocket, like when you have a hood on, if the wind isn't blowing, you can get by pretty easily without extra face protection.

[lwhikerchris]

Lots of great useful information in this thread as well as links. My 20° bag is actually a Zpacks bag and I'm very happy with it. The 40° quilt is homemade by someone from BLP.

I was out in -8° windchill temps tonight for a few hours in my setup and was very comfortable. The only thing I need is something to cover my eyes and possibly some down boots. I'm thinking a fleece headband or neck gaiter as one poster suggested.

My set up is:
ground cloth
XTherm small
Gossamer sit light pad (for feet)
Sea to Summit inflatable pillow
Zpacks 20° down bag
MYOG 40° synthetic quilt


Cap 3 bottoms
Cap 4 top
Merino hoody top
Down sweater jacket
fleece balaclava
down hat
fleece socks

[nsherry61]

. . . I was out in -8° windchill temps tonight for a few hours in my setup and was very comfortable.
Did your setup include any kind of shelter?

You've hit on one of my pet peeves. Sorry. I had a fight with my wife about this just last night.

WIND CHILL TEMPS ARE MEANINGLESS!!!! . . . Unless they are put in the context of the actual temperature and the wind speed that you are actually encountering in the exact location at that exact moment where you are currently standing/sitting/laying.

In the statement above, a -8° windchill is relevant if lwhikerchris is trying to sleep without any shelter - fully exposed. But if inside a tent, wind chill is irrelevant and it is more the ambient temperature that will determine how warm or cold he sleeps, not the wind chill. And, this matters as you test equipment to determine what environmental conditions you and your equipment can manage.

[Puddlefish]

Did your setup include any kind of shelter?

You've hit on one of my pet peeves. Sorry. I had a fight with my wife about this just last night.

WIND CHILL TEMPS ARE MEANINGLESS!!!! . . . Unless they are put in the context of the actual temperature and the wind speed that you are actually encountering in the exact location at that exact moment where you are currently standing/sitting/laying.

In the statement above, a -8° windchill is relevant if lwhikerchris is trying to sleep without any shelter - fully exposed. But if inside a tent, wind chill is irrelevant and it is more the ambient temperature that will determine how warm or cold he sleeps, not the wind chill. And, this matters as you test equipment to determine what environmental conditions you and your equipment can manage.


I also find wind chill to be an unhelpful planning indicator. I want to know how cold it is, and how windy it is. If I'm standing in my front yard, sheltered by the trees all around me, I can stand around comfortably in my jacket, I can walk half a mile away on the same day and the wind whips snow across the lake sandblasting my face. A single wind chill indicator today is meaningless to me. It's winter, I'm always going to be prepared for the wind, because conditions vary from minute to minute.

Plus, if I complain about the cold and wind chill here in NH, the Canadians laugh at me.

[Traillium]

As a Canuck with lots of exposure time in cold and windy weather, I'd point out that windchill _does_ matter in a tent or enclosed hammock.
It doesn't matter as much in a shelter of any sort as when hiking out in exposed conditions — where windchill is an important indicator (rather than a truly solid empirical measurement).
In a tent or hammock, wind strips heat away from the outside of the enclosure. That inevitably makes conditions inside cooler. This is especially true the less sealed the tent of hammock is. Total enclosure is warmer than full exposure.
Of course, this is complicated by condensation … Nothing is simple …
I'd venture that heat loss due to radiation is also a big winter issue. I'll always try to camp under the wind protection of conifers and rely at least as much on the radiation protection of said conifers.


Bruce Traillium

[Puddlefish]

As a Canuck with lots of exposure time in cold and windy weather, I'd point out that windchill _does_ matter in a tent or enclosed hammock.
It doesn't matter as much in a shelter of any sort as when hiking out in exposed conditions — where windchill is an important indicator (rather than a truly solid empirical measurement).
In a tent or hammock, wind strips heat away from the outside of the enclosure. That inevitably makes conditions inside cooler. This is especially true the less sealed the tent of hammock is. Total enclosure is warmer than full exposure.
Of course, this is complicated by condensation … Nothing is simple …
I'd venture that heat loss due to radiation is also a big winter issue. I'll always try to camp under the wind protection of conifers and rely at least as much on the radiation protection of said conifers.


Bruce Traillium

The problem is that a windchill number by itself isn't overly useful. It can be 15 degrees with a 40 mph wind, or 0 degrees with a 5 mph wind, and both have nearly the same wind chill. You'll prepare very differently for the two different conditions.

[nsherry61]

. . . if I complain about the cold and wind chill here in NH, the Canadians laugh at me.
I love Canadians.

[lwhikerchris]

Sorry, I should have specified. I was not in a tent last night, just my set up out in the open on the ground. Temperature was around 5° with some wind.

I have a shelter that I'm taking with me, a Lightheart cuben solo.

[nsherry61]

. . . I was not in a tent last night, just my set up out in the open on the ground. Temperature was around 5° with some wind. . .
Sounds like you've lined yourself up a great and flexible winter kit. Well done!

[George]

The only thing I need is something to cover my eyes and possibly some down boots.


try to adjust the hat/hood to cover the eyes

booties are too much of a one use item, besides extra socks I like insulated pants that can be pulled down to cover the feet at night

[Traillium]

The problem is that a windchill number by itself isn't overly useful. It can be 15 degrees with a 40 mph wind, or 0 degrees with a 5 mph wind, and both have nearly the same wind chill. You'll prepare very differently for the two different conditions.

Very true!

One number doesn't cut it for a multivariate activity like backpacking!

Thanks!


Bruce Traillium

[egilbe]

http://www.amazon.com/Ergodyne-N-Ferno-6970-Extreme-Balaclava/dp/B0091CC38A/ref=br_lf_m_5pjutkm62amr8k3_ttl?ie=UTF8&s=hi

breathing through a copper coil is about as good as it gets for below zero

I was tempted to get s.omething like that from Cold Avenger, today. Common sense prevailed and my gf and I aborted our hike and went to LLBean, instead. What are the chances its going to get this cold again, this year? Calling for rain and 45* on Tuesday. I can wait.

I keep telling my gf that wind chill isnt real. Its a made up number to make meteorolgy more exciting than it actually is.

[LIhikers]

..........
I need to figure out a solution for my mouth, nose, and eye area since the air was pretty cold. Right now I'm using a fleece balaclava and Black Rock down hat.

A separate down hood might help
http://www.zpacks.com/accessories/goosehood.shtml

[Venchka]

Lots of great useful information in this thread as well as links. My 20° bag is actually a Zpacks bag and I'm very happy with it. The 40° quilt is homemade by someone from BLP.

I was out in -8° windchill temps tonight for a few hours in my setup and was very comfortable. The only thing I need is something to cover my eyes and possibly some down boots. I'm thinking a fleece headband or neck gaiter as one poster suggested.

My set up is:
ground cloth
XTherm small
Gossamer sit light pad (for feet)
Sea to Summit inflatable pillow
Zpacks 20° down bag
MYOG 40° synthetic quilt


Cap 3 bottoms
Cap 4 top
Merino hoody top
Down sweater jacket
fleece balaclava
down hat
fleece socks

I don't own that much stuff to sleep in. The ambient temperature had better have been in single digits and you should have been sleeping in the open to need all of that clothing. Or you and all the other Quilt Worshippers have been fed a line of BS.
Of course, if anyone has been paying attention, Just Bill has been saying that 20 F is the break point between quilts and real bags.
I'm spoiled. I own 2 WM bags. They are the most economical sleeping bags you can buy, and the last one you will need for a given temperature range.
All that stuff you were wearing and still uncomfortable cost more and weighed more than a decent sleeping bag for the conditions you were in. The short Xtherm was obviously a waste of money.

What was the actual measured temperature? What shelter did you have?
Good luck.

Wayne


Sent from somewhere around here.

[lwhikerchris]

I don't own that much stuff to sleep in. The ambient temperature had better have been in single digits and you should have been sleeping in the open to need all of that clothing. Or you and all the other Quilt Worshippers have been fed a line of BS.
Of course, if anyone has been paying attention, Just Bill has been saying that 20 F is the break point between quilts and real bags.
I'm spoiled. I own 2 WM bags. They are the most economical sleeping bags you can buy, and the last one you will need for a given temperature range.
All that stuff you were wearing and still uncomfortable cost more and weighed more than a decent sleeping bag for the conditions you were in. The short Xtherm was obviously a waste of money.

What was the actual measured temperature? What shelter did you have?
Good luck.

Wayne


Sent from somewhere around here.


Lol, feel free to read the thread silly ****.

[Venchka]

Lol, feel free to read the thread silly ****.

I did. I stand by my earlier suppositions.
You sleep cold.
Shelter (wind proof tents) makes a big difference.
Wind chill (effect of evaporative cooling) is real. Not sure you can assign a number to it and report that number as Gospel on TV.
At 20 F and below you need one decent sleeping bag with 3-D hood, collar, foot box, plump zipper baffle and 3" loft (more as the temperature drops) over the top of you.
Adding a 1"-2" loft quilt will help a lot as the temperature approaches Zero.
Full length R-5 (min) pad below you.
Spend the whole night out. Bailing out during the warmest part of the evening is an incomplete test.
Clothing to suit personal needs.
Did I miss anything?

Wayne


Sent from somewhere around here.

[lwhikerchris]

Did I miss anything?

Yes, the whole point of this discussion.

[Venchka]

Perhaps it's the wrong point.

Wayne


Sent from somewhere around here.

[4eyedbuzzard]

I keep telling my gf that wind chill isnt real. Its a made up number to make meteorolgy more exciting than it actually is.While wind chill factor is a "manufactured number" its intent isn't to make meteorology more "exciting", even if some weather reporters choose to use it as such. Historically it got its start in Antarctica, to help in determining weather severity. It tries to approximate the actual measured air temperature that would result in the same degree of heat loss on a person due to the increase in convective heat loss due to the wind. There are many models. And a lot of variation between individuals. But it isn't just for entertainment.