Layering down equipment?

http://www.phdesigns.co.uk/product_info.php?cat=26&products_id=217

PHD in the UK do just that with their combi-bag.

I have done this some also with a Montbell UL Down Inner and a Montbell Alpine Jacket. That is warm. You almost have to do it with a thin and really puffy one.

^ I use a very similar combo- MB ex-light w/ a MB alpine light parka, the ex-light is relatively close fitting and not very thick, the alpine light is cut fuller and is meant to layer over other garments

Will R did an article some time ago where utilized a similar system- light down jacket in conjunction w/ a mid-weight parka, gives you more options if the weather is changing (like day to night :)) for not much extra weight vs one big down parka

Kevin,

People do this all the time to push the limits of whatever equipment they readily have available. I always wear my down jacket inside my down sleeping bag to boost warmth. As far as manufacturers not posting temp ratings when layering, well you have to understand that it's not as simple as a+b=c type math. Say I layer my 32 degree bag inside my 15 degree bag…how does one account for the insulation and loft that is being smooshed and losing it's heating efficiency? How much dead air space is between the two items your layering? etc etc. There are far too many variables to take into account for anyone to give a solid temp rating when layering two items. You're simply going to have to go through trial and error but have a foolproof backup plan if the SHTF, seeing as how it's winter camping you're thinking about.

I just lost a very detailed post on this :(
It's as simple as a+b=c if you use the right units, i.e., clo not temp ratings.
See the graph that Richard Nisley posted:
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=9378

I think Konrads point is that it's usually never a perfect environment and that one or more garments/bags is not at full loft and somewhat compressed, so you might want to use the a+b+c as an ideal situation and figure it's probably going to be a little less in real life, but you are absolutely spot on about adding clo values

The big benefit with layering warm clothing is that you will be relatively warm when you have to get out of your bag/quilt to pee or to tear down camp.

Having most of your insulation as warm clothing helps reduce the effect of drafts when you move around while sleeping.

I find it overall more comfortable to have my clothing providing half the warmth. The bag/quilt just adding the extra insulation needed when my body slows down when I sleep.

Walter and Mike, I agree with you both. Thanks Mike for clarifying what I meant. Controlled testing is one thing and can yield great data, but in actual practice where there are more moving parts and not all of them fit together smoothly (pinched loft, humidity, too much/too little dead air space due to movement or improper sizing, etc) will likely produce results that are below expectations. To me, its akin to the concept of 900FP down. I think there was some BPL testing which indicated that these down ratings are only achievable in the most ideal and dry conditions, whereas in real life practice the difference between 800 to 900fp is negligible, and even less resilient in maintaing loft than 700FP down.

Konrad and Mike: Yes, I'd say the theoretical rating of layered sleeping bags might be a lot better than the reality. My lost detailed post calculated 30F and 20F bags from Feathered Friends and it came to a -50F rating (with a lot of assumptions). This strikes me as unlikely, but it would work in pretty cold temps. The total amount of down was 200grams less than FF's -40 bag. I'd want to try a layered setup like that at 0F or -10F before anything colder.

A standard setup for people in New England that were poor was a down inner bag and synthetic rectangular bag with two pads underneath.

A standard setup for people in New England that were poor was a down inner bag and synthetic rectangular bag with two pads underneath.

down under synthetic is well known as the "best" option for moisture management should it be possible … thus the concept of overbags ….

a down jacket as a booster layer under a synthetic outer works very well and is quite flexible … the problem is finding a system that all fits together

Mark Compton wrote this:
"x -(70 – y)/2 = z

x = first bag (higher rated/lower degree)
y = second bag (lower rated/higher degree)
z = rating of doubled bags

**I take no credit for this equation. Had it written down from years ago.
Where? ->? "

This was in
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=56548

This seems very close to what I have experienced, though it gets off with really low temps (-25 and below.) It is within most peoples temperature comfort range. (People often differ by as much as 20F for what is a "comfortable" sleeping temp.)

I agree about a good down jacket. It is possible to get another 7-10F of warmth with one and is far more comfortable for midnight breaks and in the morning when you have to get up.

I do not hike in winter, anymore (diabetes) but I have found this formula compatible with what I did on ice fishing trips, years ago (within a broad range of about 20F.) So, this is some verification for it. Anyway, by the numbers, this is what I get for my bags: all 800FP or better down. These jive pretty much with my experience on the ice. (Note that padding will make a 10F difference but would not normally be down all by itself, assuming at least an R2.5 in more than 15F weather and R5 below you for temps less than that. On the ice I would use 4 layers of quilt, or take one of the kids bags to put on top of my two mats.)
Example:
Sleep rated: weight combined temp combined weight
0F + 40F + jacket weight: 3#13+1#11+12 -22F 6#4
0F + 40F weight: 3#13+1#11 -15F 5#8
0F + jacket weight: 3#13+12 -7F 4#9
0F bag weight: 3#13 0F 3#13
40F + 40F + jacket weight: 1#11+1#11+12 18F 4#2
40F + 40F weight: 1#11+1#11 25F 3#6
40F bag + jacket weight: 1#11+12 33F 2#7
40F bag weight: 1#11 40F 1#11

^ sounds very plausible, but I'd certainly want more then R2.5 for temps approaching 15F, my neoair is about at it's max at or a little below freezing and it's R3.2

If it wasn't compressed at all, and just followed theory, it would be:

z = x – (93 – y) (or z = x + y – 93)

93 is the temperature where clo = 0 on Richard's chart, or Ray Jardine's, or in that Mammut document http://www.mammut.ch/images/Mammut_Sleep_well_pt1_E.pdf

which is your skin temperature when you're sleeping and cool but still comfortable

if you had two bags that were 45 degrees, it would be good down to -3 degrees which seems awfully aggressive – they would probably be compressed some so it would be higher than that but it just depends on how compressed

when I wear an insulated vest inside my sleeping bag, the sleeping bag is plenty big so the vest isn't compressed and I think it pretty much follows that equation

and when I measured two test sample insulations on top of each other it followed the equation closely

Mike,
Yes, but it has been a long time since I went ice fishing…mostly dragging a tobaggan. I had the old puptent and threw down the mat over the snow before setting it up…no digging and stuff. With the quilt over the floor, another 1/2-1" of "synthetic" insulation as I remember, it was OK. We would mostly play cards and peek out the door flap every 15 minutes or so, lots of beer and brandy, hey, hey.

Wish I had a neoair, then. They didn't make them, though.