I don't think the jury is out on the benefits of vapour barriers. They are well established for use in sleeping bags in extreme cold. I've tried vapour barrier clothing and it does work when stationary in sub zero temperatures. However I found that as soon as I started moving I sweated so much that I felt extremely uncomfortable. I've worn vapour barrier clothing in sleeping bags and it feels clammy but does add a considerable amount of warmth. I've also worn plastic bags on my feet, with socks over the top and then another pair of plastic bags to keep the socks dry in leaky boots in sub zero temperatures. The plastic bags didn't last long but while they were intact my feet stayed very warm.
Right Chris, that's essentially what I had supposed in theory. My 'jury' is only debating whether vapour barrier clothing is a good idea for outdoor activities... not the principle of staying warm in still conditions.
Sorry John I misunderstood you. I reckon it would need to be extremely cold, below -25 probably, before I could wear vapour barrier clothing other than socks and gloves without getting very sweaty inside. At -10 I certainly overheat very quickly.
I always carry a Rab Survival Zone basic bivvy bag. It's a breathable pertex bag with just a drawcord to seal it around your face. It's as basic as they come but vastly better than an orange plastic bag.
Mines weighs 367 grams including stuffsack so it's not a burden to carry it. I also use it as a sleeping bag cover in colder weather.
PS: I also check the dates of the threads I reply to!
sorry John, i thought I had turned on my email function (obviously a case of computer "says no"). I was going to ask if you had tested/practised your theoretical idea on insulation in your survival bag,maybe with an immobilised limb. But later Sloth summed thing up well with:There is kits of two poly bags with the principle that you pack the space between them with moss and branches etc as insulation and then get into the inner bag, obviously this is not much use on a barren hillside with a broken leg. Which was the reason I didn't mention the two bag idea, as it is only practical if you are in fit and healthy condition. Lastly as to whether there has been serious research into differing clothing and vapour barrier idea's, well yes there has. The British army /MOD (as well as most armies I suspect) Has researched this subject for time years now, but I'm not sure how public any of the results are!. It is also interesting to note that the army has masses of really excellent cold weather gear, but they are too stingy to issue it out to the folks who need it.
Like geoff I carry the Rab Survival Zone. I find its a great reassurance knowing its in the bottom of my sack, its lightweight and extremely versitle as it doubles as a sleeping bag cover for bothying or flysheet camping and is also a bit more breathable than a plastic survial bag. and of course in really good weather you can use it as a bivvy.
I'd like to see some experimental evidence to support the suggestion that 'space blankets' prevent black body radiation in this application. Or rather, the degree to which they are effective at reducing heat loss.
I've mentioned it before, but Don Robertson, in the DoE 'Expedition' book discusses the relative merits of space blanket and polythene bag, based on research he performed at the DCTA Farnborough. Given thin polyester's poor tear resistance once a tear has started (e.g. the cover of a 'ready meal'), they found that in windy conditions, the space blankets shredded to uselessness very quickly, whilst the polythene bags continued to perform, being more robust. He cast doubt on the black body radiation effects, asking if you knew which side the metallisation was. And if you did, which side to make it face...
The earlier 'example' given, of a man dying in a polybag whilst the woman survived in a Gore-tex bag, has no other information to make any conclusion at all; body fat levels, state of hydration/nutrition, clothing, etc. Had he been a 'gentleman' and made sacrifices for her? Who knows. Whilst I have no doubt that I'd prefer to be in a Gore-tex bag in such situations, I also know that such a bag weighs about 6 times what my cheap polybag weighs, and that I'd prefer to be in a sleeping bag in a decent bivvy bag or tent...
I think that the difference between a polybag and a Gore-Tex bivi bag would be minimal if you didn't have adequate clothing. Neither of them provides much in the way of warmth, they simply keep off the wind and rain. Even with a sleeping bag you can be cold in a Gore-Tex bivi bag if the temperature falls low enough - I remember spending one night in the snow in Lapland sleeping in a -5 rated sleeping bag in a Gore-Tex bivi bag on a 3/4 foam pad and my pack (which had a padded back) under a large group shelter spread over skis and ski poles. I was wearing a down jacket and other clothing. The temperature fell to -25C and I was chilly. In the morning I shook the ice out of the bivi bag.
Rather than a space blanket there are silver sided foil bags that would be much easier to use. No thin bag is going to provide much warmth though whether it reflects heat or not. Adequate clothing/sleeping bag is needed too.
You don't have to be in Lapland, or even in the mountains, to die of exposure.
One night I pitched my tent on the towpath of the Royal Canal a very long day's walk from the centre of Dublin. It was barely above sea level, but bitterly cold and frosty. The canal was frozen, and I was pretty chilly in my tent, but bear in mind I wasn't using a winter sleeping bag or a mattress, not expecting it to be so extreme.
Anyway, the following day there was an item on the news. A woman walking home late from a party, and obviously tired, decided to get a bit of shut-eye by lying down at the side of a field just off the road, not many miles from where I was pitched. As her body temperature plumetted, she simply died in her sleep.
There's a significant psychological element to all this as well. If you pack a sleeping bag and goretex bivvy you can actually 'imagine' having a reasonable night out in the elements, meaning that you are might find yoursefl being less cautious of your timings and techniques... potentially very dangerous. Plus the additional weight of a sleeping bag and goretex(or similar) bivvy means you are more likely to need them!
Equally, knowledge is at least as useful as the kit you carry (and weighs nothing). I don't do much snow work, but I imagine that a decent plastic shovel and the knowledge of how to make an effective snowhole would be lighter and more useful than carrying a sleeping bag and bivvy. If I ever planned an extensive trip into the snow, I'd invest in some training on snow-holes first(+ avalanche avoidance and crevasse rescue).
If you have any doubt about the effectiveness of radiation shielding, try comparing how you feel standing under a flimsy metal bus shelter (on a cold clear still night) with standing outside it. My shaved head will tell you that you can literally feel the heatloss to an open sky.
I agree that spaceblankets are flimsy (hence my belief that they shouldn't be your outer layer), but even a cheap one can have some merit. The direction of the metallic coating probably wouldn't make much difference, but shiny-side-in seems the obvious choice (I'll have to think about this more carefully...). To my mind the disadvantage of a sleeping-bag shaped reflective blanket is that it cannot easily be rigged as a sunshield in hot climates, nor wrapped around two people for example. I did see a poly bag with a reflective liner on the market a few years ago but I don't remember the manufacturer???
I'm not sure if people really might be less cautious if they pack a sleeping bag and bivvy bag. I always carry enough gear (though not usually a sleeping bag) that I think I could survive a night out if necessary - I've never yet had to do so on a day out in the Highlands though I have descended after dark many times.
Snow shovels are crucial for survival in snow and I carry one whenever there's enough snow to dig into. I've spent many nights (intentionally!) in snow shelters. I'd certainly rather have a shovel than a sleeping bag. I wouldn't recommend a plastic shovel though. These are fine in soft snow but tend to bounce off hard, icy snow. A metal shovel is better.
In my opinion a metallic coated survival bag is better than a space blanket for UK use - sun shields aren't need that often!. I have one of these, called the Space Emergency Bag, I carry May to September, though I've never used it. Obviously it's much easier to use a bag than a blanket, especially in a strong wind. I have used an All Weather Blanket as a sun shield in deserts and it works well. The same blanket is tough enough to also be used as a ground sheet and is far tougher than a space blanket.
Radiation shielding can be provided by any shelter - trees, overhanging rock, bothy bag, bivvy bag, survival bag. It doesn't have to be metallic coated, though this will increase warmth by reflection.
My Emergency Bag and All Weather Blanket are made by MPI Outdoors
Hi Red Yeti, It was not the ideal comparrison to this thread. Captain paranoia also summed this above as: The earlier 'example' given, of a man dying in a polybag whilst the woman survived in a Gore-tex bag, has no other information to make any conclusion at all; body fat levels, state of hydration/nutrition, clothing, etc. Had he been a 'gentleman' and made sacrifices for her? Who knows. Whilst I have no doubt that I'd prefer to be in a Gore-tex bag in such situations, I also know that such a bag weighs about 6 times what my cheap polybag weighs, and that I'd prefer to be in a sleeping bag in a decent bivvy bag or tent.. As for the Dalton party, they were a party of rich settlers in early American colonisation by europeans. Very basically they made the massive mistake of carrying too much gear, and wanting to travel in luxury, thus they got stuck in freezing weather, and had to pitch a camp (even building cabins). The outcome was that the (fitter and stronger) men tended to die first, while the women survived despite eating less food. The case is famous (infamous) as the party turned to cannibalism to survive. with one of the surviving males boasting about being a cannibal, and threatening to eat small children, once they arrived at their final destination.. So as I said, its a poor link. What is a factor is is that women burn fewer calories than men (generally, due to difference in size) and that women also have a higher fat content than men the above factors, along with any alcohol previously consumed, or the amount of food eaten, would also be very relevent. Sorry for the short novel, But I am tired, and not being concise in my typing
The Donner Party were members of a wagon train caught in the snow in the Sierra Nevada. Wikipedia says:
"The emigrants slaughtered their oxen, but there was not enough meat to feed so many for long. In mid-December, fifteen of the trapped emigrants, later known as the Forlorn Hope, set out on snowshoes for Sutter's Fort, about 100 miles (160 kilometers) away, to seek help. When one man gave out and had to be left behind, the others continued, but soon became lost and ran out of food.
Caught without shelter in a raging blizzard, four of the party died. The survivors resorted to cannibalism, then continued on their journey; three more died and were also cannibalized. Close to death, the seven surviving snowshoers finally reached safety on the western side of the mountains on January 18, 1847.
Californians rallied to save the Donner Party and equipped a total of four rescue parties, or "reliefs." When the First Relief arrived, 14 emigrants had died at the camps and the rest were extremely weak. Most had been surviving on boiled ox hide, but there had been no cannibalism. The First Relief set out with 21 refugees on February 22.
When the Second Relief arrived a week later, they found that some of the 31 emigrants left behind at the camps had begun to eat the dead. The Second Relief took 17 emigrants with them, the Third Relief four. By the time the Fourth Relief had reached the camp, only one man was alive. The last member of the Donner Party arrived at Sutter's Fort on April 29.
Of the original 87 pioneers, 41 died and 46 survived.
I have a Vango Storm Shelter, which i must say is by far the best piece of kit i own. I first used it last February on the summit of Dreish, conditions were clear but Gale force winds turned the wind chill temp to -15ish! In days gone by it would have been a quick escape, but not this time, into the shelter, off with the mitts(yes off)and sat there snug for 20minutes having lunch whilst the wind battered against me. It even has a window so you can still admire the views? Best £21 spent, oh the Orange plastic bag is now being used as rucksack liner.
