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What Is Down Control?
Insulative down and its dead air space is responsible for the warmth of a sleeping bag. The distribution of down throughout the bag must be controlled to keep it in place and to prevent unwanted movement. Down control is achieved two ways, first, down is confined to walled baffles made up of the outside and inside shell fabrics and the no-see-um netting stitched to them. These baffle walls contain the down to limit shifting within a contained area. If baffles are too large, down can move around across a larger space. Smaller baffles keep the down within a smaller area. The second way to achieve down control is to fill the baffles dense enough so that the friction within the baffle prevents movement. Sufficient density can be seen when the shell fabric firmly bulges between baffle seams.
Relofting Tip
Relofting your down sleeping bag before a trip is a good idea and can easily be done at home. Place your bag in a tumble dryer and set it to low heat. This will allow the down clusters to open fully. Always check the inside of your dryer for hot spots that can melt the nylon shell.
Water Management
The fear of a wet bag is the most cited reason for people to avoid down. This is a mistake. Any bag that is wet is miserable to sleep in and that is why it's so important to keep your gear dry. You'll find it's a skill easier to learn than map reading. Consider all the avenues available to keep your bag dry, like tents, bivys, and proper camp placement. Then consider the number of times your sleeping bag has gotten wet to the extent that it could not be used. Catastrophic wetting is extremely rare and is an indicator of other problems. You may find that you have indeed mastered the skill of staying dry. All shell fabrics used by Western Mountaineering are treated with a surface Durable Water Repellent finish (DWR) with an 80/20 rating. This is more than sufficient to shrug off dew and condensation. And, DWR's can be easily reapplied as time wears them thin.
How To Use Temperature Ratings
Judging a sleeping bags temperature value by looking only at its temperature rating is strongly discouraged. Temperature ratings are nothing more than a rough guide and should only be used as a starting point. Also, one company's temperature rating has no bearing or relationship to another company's rating system. In fact all efforts by ORCA (Outdoor Recreation Coalition of America) and ASTM (American Society for Testing and Materials) to standardize temperature ratings have failed miserably. Why? Simply because it is your metabolism that is responsible for how comfortable you will be at a given temperature and everyone's metabolism is different. Honest! I'm not making this stuff up!
To choose the bag best for your temperature needs start with its temperature rating, then look at the loft of the bag. The more loft a bag has the warmer it will be. Next, look at the bag's Girth. This will give you an idea of a bags internal volume. A bag with a large internal volume will take longer to heat up and will be subject to more convective heat loss when air moves in and out of the bag as you move inside. This is called the bellows effect. Narrow bags or bags with a small internal volume are warmer. Also look at the Fill Weight of the bag. This will not only show how much down the manufacturer puts into a given bag, but could reveal the density of the down inside the chambers and the Fill Power of the down being used. And keep in mind that if two bags have the same internal volume, the bag with more loft will be warmer. If two bags have the same loft, the bag with the smaller internal volume will be more efficient and warmer. If two bags have the same loft and internal volume, but one has a lot more down fill by weight, then check the density of down inside the chambers and the fill power claimed by the manufacturer. Well filled down chambers provide better down control.
The Evolution of Temperature Ratings
Years ago in the early '60's, mountaineers selected bags by looking at the "fill weight". They were aware that down bags with less than 20 ounces of down were summer weight, and for winter use they would look for a bag with 35 or more ounces of down. Fill weights were used as a rough estimate of a bags temperature value. Then, in an effort to make purchases easier, temperature ratings came into vogue. However, by simplifying the process they not only introduced manufacturer interpretation, but also steered customers from understanding the mechanics of how a sleeping bag works. Since it is the individual's metabolism that heats a sleeping bag, it remains important for you to fully understand the functions of fill weight, loft, internal girth, etc. No amount of simplification will benefit the customer. Only by understanding how a bag works will a customer make the correct choice. To this day fill weights are still listed in manufacturers charts because of how useful they really are!
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