We all know the benefits of dressing in layers. I've been attempting to put the same logic to a home brew sleep system. By layering up a sleeping bag, vapor barrier, heat reflector, clothing, sleep pad and bivy sack one should be able to create a modular system which can cover a wide range of temperatures.

What I can't figure out (on paper anyhow) is what approximate rating the sum of the parts will be (in various combinations). I don't expect the whole to be the sum of the parts.

For example my sleeping bag is rated to 20F/-7C. It's going to have a heat reflective vapor barrier liner inside it and the bag will be inside an REI Minimalist Bivy...add some light clothing and a Thermarest Ridge Rest and it should be good to a rating of...well I have no idea beyond 'damn cold...I think'.

Do any of you know of any resources where there is information on this sort of thing? Or do any of you have information/opinions? I'd like to be able to figure out just how low I can go (theoretically) before I learn the hard way that it's not enough.

I do plan to test the system before relying on it...but I'm not going to wait for the coldest day of the year to do so...that could be the day I need it afterall!

I have a Tennier MSS (Modular Sleep System) which is a series of bags that are good from -10º to 50º. I should mention that the coldest temperatures that I've gotten a chance to test it in has been the low twenties to high teens, and it performed well. I had to take off my base layer because I started sweating. The highest temperature has been around 65º and at that point I left it unzipped and wide open, essentially using it as an additional layer of padding over my Thermarest.

I would like to have gotten a Slumberjack SVCSS (Slumberjack Variable Component Sleep System), which is rated -30º to 30º. However, it costs about $500.00 to $700.00 depending on whether you buy the whole system together or in pieces. That, and they were only making the MSS at the time, or they changed the name to seperate themselves from other companies.

In any case, the Tennier MSS cost me between $300.00 and $350.00 two years ago, if I remember correctly.

putting the vapor barrier on the outside of the bag in the winter is a BAD idea. All of the moisture coming off your body in the form of vapor will freeze inside the loft and if you need to use the bag for several days, your 3 pound 20 degree bag can become a 15 lbs block of ice with zero insulation.

It's the same with boots. I use Integral Designs vapor barrier booties over top of my socks and inside my big big winter boots to prevent the felt liners from getting wet and freezing.

On a side note I wonder if the a GI poncho liner would work well with my silnylon tarponcho.

Hi,

I have never used a vapour barrier inside my sleeping bag or boots; does it not make you clammy, wet and eventually cold?

I would appreciate the details on this idea as it may be a trick I could use.

Thanks,

Mike

It does make you clammy...which is why they're not popular despite their benefits.

The benefits far outweigh any discomfort. They keep vapor from condensing and freezing in the bag, they help prevent moisture loss at night as when skin is moist (or at least in a super high humidity environment), the body won't sweat as much, retaining it where it's needed, it also keeps the bag 'fresh' by keeping smelly sweat out of it.

I sweat...a lot. My feet sweat so bad that if I don't use Drysol (prescription strength anti-perspirant 20-30 times stronger than over the counter stuff) to prevent them from sweating the sweat glands rupture due to over activity (Then I have to the other prescription for Cortizone cream to keep my feet from cracking and bleeding). All my life I struggled with my feet freezing in even mildly cold temperatures...it's one of th reasons I gave up skiing when I was younger. Managing the sweat helped an amazing amount. Medication, wearing proper socks in proper layers, etc. When I started wearing the vapor barrier booties, all of a sudden my feet were NEVER cold (I first tested with bread bags based on internet research). When I realized how well it worked, I ponied up for the silnylon version from Integral Designs ( http://www.integraldesigns.com/product_d...producttypeid=1 ).

In the past I've had similar issues with down bags. With a modern synthetic bag the loft itself is waterproof and can still insulate when wet...but in the winter this moisture freezes and becomes dead weight. I've had this happen before too though it's far less common in only moderately cold temperatures. The Integral Designs vapor barrier for long bags is upwards of 60 bucks so I'm DIYing it by slightly modifying an AMK 2.0 Bivy to do the job. It won't be perfectly sealed at the edges but it should be sufficient...and has the added benefit of being a very efficient heat reflector as well.

To combat the clammyness I've dedicated some MEC silkweight micro wool long johns, long sleeve shirt and some fox sock liners to sleep wear. Very lightweight and compressable, they add very little weight to the system (handy to have around as backup clothing too). They add insulation and wick moisture away from my body so cut down on the clamminess. The wool doesn't hold water very well and even if it does, it's dedicated to sleep so it's a minor inconveniance...I'd rather have a few ounces of wool frozen than my entire sleeping bag. I keep them in a ziplock to prevent the moisture (and potentially stink) from getting into other stuff in the system.

Below are a couple of sites with information about vapor barriers and their history. Some of it might sound like voodoo science but regardless, it works.

http://www.warmlite.com/vb.htm
http://www.netbackpacking.com/vapor-barrier-and-radiant-barrier-liners.html

Hi Hacksaw,

Thanks for the detailed information on vapour barriers.

I do not have the sweating problems you have but do find that my boot liners are soaked at the end of each day. I will give the vapour barrier between the socks and liners idea a try this winter to see how it works for me.

I remember Michel Blomgen used plastic bags in his Sorel Caribou Boots in this way in one of his Swedish video's (may have been #4, "Cold of the Night").

As kids we used plastic bags in this way to keep our feet dry when our boots were not waterproof and we were going ice fishing in the slush.

I do not know if I could get used to being clammy when I am trying to sleep, I will have to try it out. I do usually sleep in some kind of clothing in my sleeping bag as I have found that it helps with that cold draft feeling.

The Canadian military cold weather sleeping bag system has a cotton liner in the bag next to your bare skin, could this be to absorb the sweat produced and prevent it from saturating the down insulation? I thought it was just to keep the bag clean but there may be another purpose. I always thought cotton was an odd material for this use but perhaps there is a logical reason.

Mike

Another sleeping system : check KIFARU's Regulator system ...

They even have sleeves, to use part of the sleeping system as a jacket.

Sleeping bag temperature ratings are about as honest as car manufacturer's gas mileage ratings. First, they are taken INSIDE a tent and usually involve a formulae involving water bottles. I don't know about you, but I am not a water bottle. IF these ratings were even remotely accurate, Every individual still has a different metabolism and body mass. The only worthwhile testing medium is to take a bag of given loft and sleep in it at various temps.Vapor barrier systems do work with the caveat of creating a swamp environment. The problem is upon leaving this micro environment your body immediately undergoes a very rapid cooling off as all that lovely sweat evaporates. In a survial situation with a body already taxed by various stresses this can prove deadly. Not to bore anyone repeating vendor references, but read the information on www.wiggys.com Jerry is VERY opinionated to the point of combatetness. He also has some pretty compelling arguments and information.

There are just too many variables in play to come up with a number that means anything.
Hydration/dehydration level, air humidity (huge factor), air movement, thickness of pad, sleeping surface temp and conductivity (rock, snow, dirt?) . . . finally, some people seem to sleep warmer than others in general and no one knows why.

You will sleep warmer if you've eaten, colder if you have not. The menu also affects nighttime metabolism, I believe . . . fats good, carbs not so much.

If you're physically exhausted you will sleep colder.

There is no standard system of measurement because of all these things. Sleeping bag manufacturers have to put a number on their bags to sell them, but the methods they use are all over the place. Some use water bottles, some use dummies heated to 98.6 degrees, some seem to guess. Kelty is wildly optimistic, Western Mountaineering is pessimistic. The two things manufacturers do in common are (as someone else here noted) assume you are in a tent and have a ground pad. So, that would seem to remove the ground pad and bivy from your calculations because they are already accounted for in the ratings.

You just have to play with it and tinker. Sleep in the yard in all sorts of weather until you come to some kind of comfort zone.

For me that arrangement would take me to zero degrees if it was a Western Mountaineering bag. With any other brand, all bets are off.

Chris brings up a very good point. If you wake up wet and you need to go outside to change, it can be a deadly maneuver. You need to be organized and you need to be quick. I've gotten pretty good at changing inside my sleeping bag...at least partially.

This is can be where good shelters separate themselves from great shelters...purchased or man made.

Does anybody have the proper wiggies link? Chris's isn't right and I'm curious to read Jerry's thoughts.