some food for thought from Andy Kirkpatrick
Synthetic sleeping bags have always been the poor relation of down, with even the most high tec fillings being far inferior to the lowest quality natural alternative (feathers). Synthetic fillings were an off shoot of the carpet industry, with hollow fibres not being developted for superior warmth, but so as not to show the dirt in capets so readily. Companies like Dupont introduced the first commercial synthetic fillings several decades ago, but these bags have remained at the bottom end of the sleeping bag market, used by car campers, caravaners, students and general normal people. The reasons for this is price and performance. A synthetic bag, even the the most state of the art, costs considerably less to manufacter then that of a standard down equivalent, making it the choise for thoes on a budjet or those unintrested in high performance. This price difference is due to the high price of down and the relative simplicity of synthetic sleeping bag manufacter. A synthetic bag does not require traditional baffles, which must be carefully sewn and hand filled, allowing simpler and faster techniques to be used. The most common construction is to simply have a sheet or wad of insulation, which is held together on a light scrim, that can be cut into a mummy shape and sandwiched between the shell fabrics and simply sewn together. Other more advanced techniques include shingle construction, were overlapping strips of insulation are sewn into the inner and outer of the bag, reducing cold spots and increasing the overall intergraty of the insulation. Quality of filling and construvtion does vary considerably between the high end bags and the mass produced ‘Argos’ moonbag, but all are consideably less complex then a down bag.
"I'd blagged the bag intending to use it for a couple of weeks winter camping in a portaledge on the Grandes Jorasses, unfortunately that didn't pan out, and so it was all I had for a super alpine assault, something that at the time I thought it was particle unsuitable for. Packing the night before we left for the mountain, I gazed down at the large bulging stuffsack beside my pack. Instead of the usual minuscule down bag, compressed to the size of a micron within the tight bind of its compression straps, I’d been lumbered with something that looked more like a medicine ball. The thing was enormous, packing down to about the same size as a small fitted kitchen - or about the same as two 1000 gram down bags. Luckily it was only about a third heavier then an equivalent down bag, even though it looked like it should weight far more."
One of the main draw backs of synthetic bags over down has been the comparitevly short life of the insulation, with a single down back outlasting two to four equivalent synthetic bags. What happens is the insulation value of the bag slowly decreases with use, caused by the wadding not bouncing back to 100% after repeated compression. The insulation can also be effected by the fibres being torn if handled roughly, or washed and dried incorectly. There are also a lot of very poor fabrics on the market that although look and feel almost like down, soon collapse. This is due to their fine and delicate man made construction not being resisiliant enought to cope with the general rough and tumble of outdoor use (wear and trear, washing etc). For many years the bench mark insulation was Polargaurd, now upgraded to Polargaurd HV, which although not the lightest fabric on the market is one of the most robust. If compression is applied only for transportation and not storage (put it under your bed in a pillar case) then a well constructed Polargaurd bag’s insulation seems to outlast most other fillings (as the fibres loose their springiness and loft), this is probably due to the fibres being more robust then the ultra lite compitition . Remember that no synthetic bag will loose all it’s insulation value, only a percentage of it, because the insulation comes from the amount of air trapped between the inner and outer fabric and there will always be some loft. If you find your old sleeping bag has cold spots then it’s probably due to the scrim being torn (hold it up to the light to check).
"Carrying a single rucksack with both our sleeping bags stuffed inside we scampered up the face. The ‘sack was of the expedition rather then the French verity, with most of it's massive capacity being taken up by my pit. My partner’s bag was a custom built expedition down design with a waterproof outer and water-resistant inner, complete with a bivi cowl. The whole thing fitting into a stuff sack the size of a small loaf of bread. Very Mark Twight. You can imagine what he said when I showed him what I’d be bringing along"
Even though synthetic bags have several drawbacks they do have one major advantage over down. The insulation is far less effected by moisture, a big advantage if you live in a maritime climate like the UK. If your down bag becomes soaked it looses virtually all it’s insulation, plus it’s hard to dry out properly or quickly – especially in the field. A synthetic bag on the other hand loses perhaps a third of it’s insulation when totally saturated, but will dry far quicker due to the water resistance of the fibres, and the fact that the bag will still insulate the user, who’s body heat will in turn dry out the bag. It is perhaps for only this one reason that synthetic bags became popular with high performance users, who needed bomb proof dependable insulation in order to survive in ‘down hostile’ environments. Sailors, big wall climbers and cavers all excepted the drawbacks associated with these bags because in the most hostile environments nothing else would work. Himalayan climbers also began using synthetic bags as covers or ‘overbags’ to cover their down sleeping bags, finding this way the dewpoint (the point at which the warm moisture vapour from the body turns back into water) formed inside the overbag, not in the down. Never the less, for the majority of users synthetic bags were too bulky and heavy for anything but car camping.
"As usual, and inconsiderately, a cold day turned to a colder night far from any prime camping spots, forcing us to chisel out a bed of ice for our frozen backsides. Because of our precarious position I had to get into the 'behemoth' with my boots on, carefully removing my crampons as I did so (Good tip that). The first thing I noticed was how much roomier the bag was compared to my current featherweight down model, obviously accounting for some of it's weight. No more agonising cramp as I removed my inner boots, and that terrible claustrophobia, caused by squeezing yourself along with several layers of bulky clothing into a narrow nylon tube filled with feathers. You see it's ok designing and choosing bivi gear in the real, warm, world, cutting bags thinner to save weight and reducing the insulation in order to shave those few grams, but up there you realise that some things are more important then the turn of the all important hand on the kitchen scales. The other thing I noticed was I'd managed to bring several shovel fulls of snow into the bag with me. Usually this would result in dread 'damp down' panic, but all I had to do was unzip the foot section of the bag and turn it inside out, shaking the snow into the bottom of my bivi bag. After a fine alpine meal fit for a mouse, I settled in for the night, slings rapped around my knees and shoulders, strangely comfortable knowing I didn't have to go to sleep with the usual down bag paranoia."
Then a few years ago there was a sudden influx of new insulations from several companies. Thies fillings, unlike the first genration fibres, had been spesificaly designed as high perforamce insulators. Companies like Ajunalak, Snugpack and Mountain equipment had already helped elavate the synthetic bag out of the performance doldrums, and now new fillings came along like Microloft, Primaloft and Liteloft, that banished the old image of the traditional mouldy synthetic bag forever. Of these fabrics Polagaurd 3D was perhaps the best (well, most widely used anyway). At the time 3D was the most advanced insulation, giving excellent weight to loft, fair compressibility and a good insulation life span. Polagaurd 3D had finally given manufactures a toe hold in the ‘real’ sleeping bag market, with 3D offering a similar performance to low quality down (450 fill power). Giving all benafits of synethic will less of the assocated drawbacks.
"I woke to a Niagara of snow, a storm of biblical proportions that flooded snow down onto us in waves. Seven hundred metres up the ice face it felt as if we were in the Gods, and what a show. My partner had turned into a snow banked, frosted blood red slug, while I tried to remain composed in my seat under the weight of bullying snow. I shouted we'd wait two hours - unsure we could - until we abandoned our posts and tried to escape. The weather only got worse. Everything was full of snow, and packing to leave was a nightmare. I stuffed my bag sans compression sack (I never did find it) under the protection of our bothy bag, yet it still went away covered and filled with snow, which I knew would soon be melted by my residual body heat inside. All I could pray for was that we wouldn't have to bivi again."
Once the big boys like The North Face, Marmot and Mountain Hardware began pushing their non down bags as viable down alternatives, adding high performnace shells and improved quliaty of contruction, then synthetics finaly began to be taken more serously. I know several climbers who tried out the new generation bags and all reported that perforamce was better then exspected, and although one climber used a model all the way up to the South Col on Everest, most reported that becouse of the weight increase, these bags were best used for summer to autom use, as winter weight bags were far two bulky and heavy. Saying that, I’ve been testing a 4 season bag that weights 2300 grams, that seems to provide about the same perforamce as an 800 gram (fill weight) down bag (1600 grams total). The differnce is that I can use a featherweight bivi bag (300 grams) rather then a fully waterproof Gore model (700 grams), which makes things a little more equal. Also after several nights of harsh camping the down bag generaly weights more due to moisture trapped in the down.
"Twenty hours latter we staggered (or did we crawl?) into the hut below the mountain. The initial warmth of escaping from the viscous winter wind soon passed, proof of it's lack of insulation the thick drifts of snow that carpeted it's kitchen and hallway. My partner pulled out his bag and looked at it dismayed. His once huge bulging bag of red hot warmth had been reduced to a pathetic flaccid and wrinkled wet rag, it's deluxe fill of feathers transformed into soggy Wheaterbix. A pile of soiled and musty blankets would have to do. Expecting to see something equally as grim I pulled out mine next and was astounded to find that the soaking had had virtually no effect whatsoever. Sure the bag was wet, with snow still climbing to the inside and outside. Giving it a quick shake I pulled off my boots, through my inner boots inside and crawled in after them."
So am I advocating a complete turn around, with down being resigned to history like moleskin trousers and Fur lined boots? Of course not. Unfortunatly for the poor duck and goose their feathers are far from being copied by man, afterall it took nature several million years to develop it’s complex construction, and I exspect we’ll see artificial intelegence cracked before the silicone feather. Down is still the lightest, most longt lasting, and sexy insulator, having that ‘ooooh’ factor that material sceice has yet to match. For most mountain sports a quality down bag, when used in conjuction with common sence and good preventave ‘wet down’ methods, is still the top dog. But for thoes who like to sleep, bivi or crash out in the worst conditions, either ntensionaly or otherwise, modern man made fillings are the only way to go. In the short time that I’ve been using synthetic bags I’ve been saved by the fillings robustness several times. Admitidly a synthetic allows you to become more lazzy and less attentive, but on a few accasions, like biving under streams of spindrift, or when you forget to close you haulbag and a sudden freak storm fills it up with water, no amount of provention would have allowed a down to survive intact. Personaly I don’t mind shouldering the slightly heavier bordon, or carrying a larger rucksack to acomidate it’s bulk, becouse I like the fact that I can have confidence that no matter what, my sleeping bag will not let me down.
"In the morning I woke to the sound of the rescue helicopter landing on the glacier outside, touting for business. I felt the inside of my bag and found it was totally dry, along with my clothes. I looked over to the sorry mess of blankets and the wet rag draped over it and realised I'd learnt a valuable lesson. Perhaps in the mad scramble for sexy light weightness I and everyone else has forgotten the most important function of gear – not that it must weight nothing, look good and be cheap, but that it must keep you alive and increases your survivability. After all isn’t survival the name of the game? With that thought keeping me warm I turned over and fell back into the kind of sleep only the condemned who have received their pardon can enjoy."
THE SCEINCE BEHIND SYTHETICS
The reason down is such a great insulator is becouse of it’s high surface area to volume ratio, with it’s filimets being as small as 7 microns (a humain hair is 50 to 150 microns). The air trapped on the surface of thies filimens is more important then the air trapped between them (that’s why card board is a better insulator then steel) and so when you consider the surface area to volume ratio of such a delicate natural wonder compared to the unsuptle man made insulator we can see why synthetic fills will take a long time to catch up. There are two basic types of synthetic fill: short staple, in which the individual fibres are a few inches long, and continous filament, or long staple, in which the fibres can be up to 500 miles long!
Short Staple filling is made into sheets of baffling, with the fibres beingh bonded together using heat and resins onto a thin paper like scrim. LiteLoft (15 microns) and Primaloft (7.5 microns) are the two main high performance Short staple fillings. Primaloft is prehaps the best we have achieved so far in man made down, but due to it’s high cost only seems to appear in clothing. LiteLoft is cheaper version and is found is many sleping bags. Unfortunatly it is heavier and performce poorly when compared to the other fabrics on the market.
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Topic: Synthetic v down (reprise) (Read 4334 times)