I find the Snugpak Sleeper Extreme to ba a good bag for winter. I have never used it in sub-zero temps but found that in the low plus temps I was too hot in it while in a bivi bag and clothed (I had to take clothes off to sleep comfortably) so I would be happy to use it into the sub-zero temps.
Need a warm sleeping bag
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I think it is much more complex than has been intimated. Here are some points to consider:
Heat Source
- our body produces heat by digesting food and other muscle movements like shivering or jogging.
- Perhaps by stripping off some people have more room/freedom to move and create more heat.
The heat we generate needs to be transferred to our extremities (hands and feet) from your main body trunk by our blood when it is pumped round. When we are cold our bodies will restrict the blood flow to the extremities to protect the main core and the brain, this is why your fingers go white and end up with frost bite in extreme circumstances.
- If your clothing is tight/twisted/restrictive it may restrict your circulation and make parts of you feel very cold.
Methods of Heat Transfer
Radiation - more relevant for higher temperatures (You've never warmed your hands 3 feet away from your mates face have you)
Conduction - generally if a material is squashed to make it denser then conduction becomes more important
Convection - when air is heated, it's density becomes lower and it rises E.G. the hot smoke from a fire rises.
Forced Convection - Moving air carries heat away from the skin much quicker than still air - Wind Chill Effect
The Bellows Effect - When in your sleeping bag and you haven't tightened the neck baffle, when you move you force warm air out and then cold air gets sucked back in (Similar to breathing out warm air from your lungs and then breathing in cold air from outside)
What is insulation?
As said above, moving air carries heat away so we trap it in little pockets. This is the same whether it is down, synthetic sleeping bags, fleece blankets or closed cell foam mats. The thicker the layer of still air, the more resistant it is to letting the heat escape.
So if your insulating layer is not allowed to loft (I.E. it is squashed into a thinner layer) IT WILL BE LESS EFFECTIVE.
Your down bag is crap where it is squashed thin by your body weight, this is why you need a sleeping mat which is resistant to being squashed flat E.G Foam mats or Self Inflatable mats which don't collapse flat because the air is trapped inside.
Perhaps if you are a large person & your sleeping bag is a tight fit, or when trying to wear too many clothes or have one sleeping bag inside another you may be squashing the insulation of all of your layers reducing their effectiveness.
You wouldn't put heavy wool blankets on top of a winter Down bag because it won't be able to loft properly.
Obviously if you have plenty of space in your bag then using a down jacket as a blanket either inside or on top of your bag will increase the insulation level.
Flip side, if your bag is too big then you have lots of air inside to heat up !
Get a smaller bag, tie off the end if it's too long or bring a blanket inside the bag.
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People have mentioned that sleeping in skivvies enables you to 'warm the bag' or 'warm the air in the bag'.
This seems counter intuitive, warming the bag means you lost heat from your body to do so!!!!!
Maybe this isn't so bad, you lose this heat when you first get in your bag.
It's good to have something to eat before going to bed as the food provides energy for your body and the act of digesting it produces heat itself ( stomach muscles pummeling the food).
Add in a few sit ups when in your bag and you have generated enough heat to create a warm environment in the bag.
This would mean your extremities which are vulnerable to the cold are now getting more benefit from shared warmth E.G. Mittens are warmer than gloves partially due to less surface area, freedom to move and shared warmth.
Wearing Clothing in your Bag ?
As above - Tight, Restrictive clothes are bad
Wet clothes = Very Bad, it takes a lot of heat to evaporate water. It will draw that heat from you !!!
In extremes the water will freeze in your insulation rendering it useless. Wet down won't loft and becomes useless.
Bulky Clothing may squash the bags insulation and vice versa meaning you may have two ineffective layers instead of one good one.
So You can wear Tomorrows unworn dry baselayers or similar and a hat.
Someone mentioned sweat, we perspire all the time even when sat still, this is called insensible perspiration and can build up in your clothing. Wool can absorb a good amount of water whilst retaining it's insulative properties. Your sleeping bag however won't like moisture building up inside it though. In Arctic conditions it is common to use a vapour barrier - basically a binbag to trap the sweat next to you and prevent it getting in the bags insulation layer. It also means that the sweat draws less heat from you to evaporate.
The neck and hood baffle/drawcords are important - learn how to use them to prevent the Bellows Effect.
Also Alcohol is a Vasodilator - fancy word for the blood vessels open up allowing the blood close to the skin (Your skin looks flushed/pink, as the blood carries heat around the body a lot more heat is lost from the skin. You might feel warm (beer coat anyone
) but you are actually losing more heat than usual. Your body wants to go the opposite way in cold weather by reducing the blood flow to the skin to conserve heat making you look pale and have cold fingers and toes.Basically, I don't think there is a right or wrong answer. EXPERIMENT FOR YOURSELVES and stop arguing
We are have different body shapes and sizes, rates of metabolism, Sleeping Bags, Sleeping Mats, Eat different foods at different times.
Anyone have any other theories ?
I'll edit this later to try and make it more readable
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Just wanted to say thanks for posting that Fizzy; I'm having one of those mate, cheers!
No problem. It looked a decent bag for the price so let me know how you get on with it, as I also recommended it to a mate of mine, he just hasn't bought it yet
A question I've thought about,
If down bags can compress so well, why is the old 58 down bag so bulky?
If down bags can compress so well, why is the old 58 down bag so bulky?
Just a thought...
When the Mountain Rescue folks find a person suffering from exposure, do they get them to strip off before they stuff them in a sleeping bag?
Z
They used to strip you if your clothes were wet ( which they usually are in an exposure situation). now I think they wrap you up in a blizzard survival blanket without stripping you..........If the Innuit found you on the ice they would strip you & themselves naked & lie with you under animal skins until you warmed up.....
The 58 pattern sleeping bag is not just down, there's quite a lot of feathers in there too which don't compress as well.as down............it's also partially rubberised ...hardly compressable.
& not forgetting, the military like big & bulky, which often equates with robust.
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army issue dude, warm robust, i have used them for years and they are awesome, 1 problem though, they are rather bulkey...
It's the mittens vs gloves thing, isn't it?
I strongly suspect that you might *feel* colder wearing your clothes, but actually you aren't losing as much heat.
Also, if the heat from your torso isn't reaching your extremities (i.e. your arms and legs are losing more heat than they gain), your body reacts by reducing bloodflow to the extremities, making arms and legs feel even colder.
I strongly suspect that you might *feel* colder wearing your clothes, but actually you aren't losing as much heat.
Also, if the heat from your torso isn't reaching your extremities (i.e. your arms and legs are losing more heat than they gain), your body reacts by reducing bloodflow to the extremities, making arms and legs feel even colder.
I was in the Arctic the other year, all the instructors told us to strip off and sleep naked, i did, and was warmest out of everyone in my tent and we went well below -20, some of the guys ignored this advice and were constantly complaining of the cold.
its your bodies heat that warms the sleeping bag up and gets trapped by the bags filling, the only time i will wear clothes in my sleeping bag is when i am hiking with an ultralight summer sleeping bag and its really cold, even then the only clothes i will wear are a PHD down ultralight smock to add to the bags down, but in a decent rated bag, you dont need clothes and will be warmer for it,,, just my opinion, but if you disagree, your clearly a softy girlie type who should be wearing a bra in their sleeping bag will doing their makeup while reading about big brother in a girlie type magazine and dreaming about changing your name to Nancy Mcgirlie pants....
its your bodies heat that warms the sleeping bag up and gets trapped by the bags filling, the only time i will wear clothes in my sleeping bag is when i am hiking with an ultralight summer sleeping bag and its really cold, even then the only clothes i will wear are a PHD down ultralight smock to add to the bags down, but in a decent rated bag, you dont need clothes and will be warmer for it,,, just my opinion, but if you disagree, your clearly a softy girlie type who should be wearing a bra in their sleeping bag will doing their makeup while reading about big brother in a girlie type magazine and dreaming about changing your name to Nancy Mcgirlie pants....
I was cold last weekend but didn't fancy getting naked as by the time I got back into my hammock I would have caught hypothermia...
Hammock sleepers are exempt from the Nancy Mcgirlie pants name as they have a problem with cold underneath them unless they have the underblanket, next time your out, no matter how cold it is, give the naked sleeping thing a try, it really works well, just make sure you have all the baffles tight at the neck of the sleeping bag to keep the heat in.
Indeed, but then it's the fact that you've lost that heat from your body in the first place. Perhaps it's down to the feeling of being warm over actually being warm? Just to add more fuel to the fire, I read somewhere that it's recommended to be naked in a down bag but not synthetic...
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