A Good Night’s Sleep. Part two.
Sleeping bags for backpacking.
Much of what was said in part one of this article https://www.charlescamping.ie/store/sleeping-bags-family-camping with regard to choosing a sleeping bag for family camping holds true when it comes to bags suitable for those people who want to traverse mountains or complete multi day walking trips. The EN13537 rating is still the gold standard for an accurate assessment of how warm the bag will keep you and the two materials used for insulation are still down or polyester.
For anyone who wants to carry a sleeping bag and other gear, in a rucksack, the weight and bulk of the bag now become very important and, at least to some extent the price becomes a secondary issue. A rough rule of thumb when buying a backpacking bag is to assume that if a bag is half the size then it will be twice the price. If it is down rather than synthetic it will be again be around twice the price. Bear in mind that paying more money doesn’t mean that the sleeping bag will be warmer. What it does mean though is that for a given temperature rating, the more expensive bag will be smaller and lighter. Like many things in life buying a high-end sleeping bag for a big trek or expedition is often a case of ‘Pay more, get less.’ In order that the smaller, lighter bag really does do the same job as the bigger, cheaper one, designers have to be somewhat more creative about how the bags are constructed and they usually use a superior grade of insulation. I won’t go over issues regarding the shape of the bag as almost every bag in this class is a mummy shape. The extra thermal efficiency is essential here and all manufacturers let form follow function and go with the warmest shape.
There are no changes to the base filling materials used in these bags compared to those for family camping. Polyester and down bags are your options. Down becomes more popular as the temperature drops or the distance of the trip increases. It gives the most warmth for the least filling. There are some down and feather mix bags on the market but the performance is lower and if the price matters then a good synthetic will outperform a cheap down bag which is bulked up by low performance, stalky feather. The synthetic bags also move up the evolutionary ladder a bit. The insulations used here will all be able to trap more air than standard polyester wadding and so less insulation is required to achieve the same result. They may be laminated in place rather than stitched which reduces heat loss and pack size. As mentioned earlier the whole idea is to get the least bag that will do the job. Methods vary but ultimately the shape of the bag and the insulation will be pretty similar in comparison to the family camping bags we looked at previously. If this is so then how do manufacturers achieve the results that they do using mostly the same materials?
The first part of the answer is in the lining and outer fabrics. These are usually higher quality and thinner than those used for campsite bags. Some have an outer fabric so thin that the insulation is visible through it. These are quality materials, with a relatively high tear strength so that even in the thinnest versions they don’t just fall apart after very little use. Do though, bear in mind that they will still, probably, be less abrasion resistant than thicker fabrics. Even the lightest fabrics though will only save a few extra grammes. The real difference lies in the next section.
In the Family Camping area, we saw that most bags were single layer ‘Stitch through’ or double layer ‘Offset baffle’ construction. One of those two methods of manufacturing would be found in almost every bag on the market. For backpacking and specialist bags the field expands somewhat. Both down and synthetic bags share similar constructions often both depend on isolating insulation so that it can’t shift. Traditionally this is done through the use of baffles.
All down and many synthetic bags are made up of hollow, fabric spaces packed with down or other insulation. Like little polyester tubes filled with fluff. These are called baffles and are the same as the baffles around insulated jackets. They keep the insulation captive and prevent it moving around thus keeping the level of warmth consistent. There are loads of baffle options but the simplest is, once again, the basic ‘Stitch through’ construction. Used mostly on warm weather bags or compact gear for travellers and adventure racers. These are pretty minimal, ideal for hostelling around the tropics but not great when the weather turns chilly again but if you are keeping your luggage lightweight for a trip to Australia then pretty much ideal. If you use this kind of bag on a winter trip in Kerry then you are probably going to be very cold and uncomfortable.
Exactly as the name suggests these are square baffles filled with insulation. There is no stitching which goes all the way through so cold spots are massively reduced. There are also slant wall box baffles which are basically the same but with the vertical walls angled.
V- baffles or Trapezoid baffles.
Two similar but not quite identical takes on baffling. Both improve the efficiency of the insulation by angling all the baffle walls rather than leaving them vertical. This might mean a slightly lighter bag or one with a smaller pack size.
Some companies use vertical baffles in torso areas and others have separate side baffles and all of these options work. If one style was clearly superior then it would be universally applied and the others would die out. All options at this level are good but none are perfect for everything or everyone.
Shingle or Wave.
Used in higher end synthetic bags. Once again these are ways of reducing heat loss through any vertical stitching. The layers of insulation overlap like roof tiles and so trap more air for less weight. The Wave version squashes a longer length of insulation into a space and this again produces a slightly warmer bag.
This is a relatively recent way of producing sleeping bags which eliminates a lot of the stitching by bonding the insulation layer to the fabric layers rather than holding them together by sewing. Using less stuff means that a bag can be lighter and smaller for a given temperature rating.
Most technical bags use differential fill which basically means that a greater proportion of the insulation in a sleeping bag is on the top rather than the bottom. The reason for this is that what is underneath you gets squashed anyway and so doesn’t contribute very much to the warmth. A good sleeping mat takes care of the underneath and insulation can be deployed where it will do the most good. We will look at mats in the last part of this series. If your bag contains, for example 400 grammes of goose down and the fill is the same all round then possibly only 250 grammes of down is keeping you warm. The rest is squished into uselessness. If more of the down is put into the top part of the bag then the latter figure may climb to over 300 grammes and the bag will feel warmer despite having no extra insulation. Thermarest are amongst a few companies who produce a range of sleeping bags for ultralight campers which have no underside at all and rely entirely on the sleeping mat for ground level comfort and insulation.
As in the previous article we will look at a series of bags and how the temperature rating changes with the spec. I will start with the Nitestar range as a familiar basis for comparison.
Nitestar Alpha 250. Comfort rating 2 degrees. Transition rating -4 degrees. Weight 1.65 kg.
Nitestar Alpha 350. Comfort rating -1 degree. Transition rating -7 degrees. Weight 2kg.
Nitestar Alpha 450. Comfort rating -4 degrees. Transition rating -11 degrees. Weight 2.3 kg.
From the same source we can look at the Ultralite Pro range of synthetic bags.
Ultralite Pro 100. Comfort rating 8 degrees. Transition rating 4 degrees. Weight 900 grammes.
Ultralite Pro 200. Comfort rating 4 degrees. Transition rating -1 degree. Weight 1.1 kg.
Ultralite Pro 300. Comfort rating -1 degree. Transition rating -6 degrees. Weight 1.35 kg.
Thermarest Saros series of synthetic bags covers a similar range of temperatures and weights.
Saros 32F. Comfort rating 5 degrees. Transition rating 0 degrees. Weight 1.06 kg.
Saros 20F. Comfort rating 0 degrees. Transition rating -6 degrees. Weight 1.46 kg.
Saros 0F. Comfort rating -10 degrees. Transition rating -18 degrees. Weight 2.24 kg.
Checking out some down equivalents gives us the following data. Bear in mind the number in the model name is the approximate weight of down, in grammes, in the bag rather than the ‘weight per square metre’ used for synthetic fillings.
Venom 200. Comfort rating 9 degrees, Transition rating 5 degrees Weight 700 grammes.
Venom 400. Comfort rating 2 degrees. Transition rating -4 degrees. Weight 1 kg.
Venom 600. Comfort rating -3 degrees. Transition rating -10 degrees. Weight 1.25 kg.
Thermarest Questar 20F. Comfort rating 0 degrees. Transition rating -6 degrees. Weight 990 grammes.
More advanced bags offer similar levels of insulation and sometimes a great deal more than the equivalent in the Nitestar range. Whether they are worth the extra cost is down entirely to personal usage. The further you intend to carry it the lighter you will want it to be and therefore the more you will have to pay. As I mentioned in the previous article nobody at this level manufactures awful sleeping bags. People camping in remote or extreme situations need to be confident, not only that they survive the night in safety but also that they sleep well. No trip goes harmoniously when people regularly wake up cold and grumpy. People like me who enjoy debating the minutiae of outdoor gear will pick over tiny details and have our own preferences but companies never want to be seen to be killing off their customers.
If you are looking for something in this area I would recommend getting into a bag and trying it for size before heading off anywhere. The right choice will probably just feel better and so long as the temperature rating fits your requirements the bag will perform just fine.
The last part of this series will be along shortly and will look at sleeping mats and camp beds.
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