In Part I we discussed the first step in selecting a sleeping bag – choosing down or synthetic insulation. If haven’t already, be sure to read that post. Now, let’s move on to some other factors to consider when selecting a sleeping bag.
The temperature rating of a sleeping bag, a “20 degree” model for example, didn’t used to mean much, really. Most sleeping bag manufacturers were more than optimistic with their ratings. If you picked a 20 degree sleeping bag off the shelf it may keep you alive at that temperature, but it certainly wasn’t going to keep you comfortable.
These days, many of the best sleeping bag manufacturers have begun rating their sleeping bags according to “EN 135227” testing. These sleeping bags are typically referred to as being “EN Rated”. The EN testing system uses a controlled environment and a mannequin equipped with multiple heat sensors to test the sleeping bags in a controlled and standardized environment. The EN Rating yields three ratings: the EN Comfort Limit, the EN Lower Limit, and the Extreme Rating.
The Comfort Limit is based on a standard woman having a comfortable night’s sleep. The Lower Limit is based on the lowest temperature at which a common man will have a comfortable night’s sleep. The Extreme Rating is the survival rating for a standard woman. For example, the Sierra Designs Zissou 23 has an EN Lower Limit (men) rating of 23, whereas the EN Comfort Limit (women) is 34.
Obviously everyone has a different comfort levels and tolerances to sleeping temperatures, so the EN ratings aren’t perfect, but they are a very welcome addition to standardize ratings across manufacturers. (I have personally found EN ratings to be quite accurate.)
Other factors that can affect the perceived warmth of your sleeping bag include the shelter that it is used with, the sleeping pad that you use to insulate you from the ground, the clothing that you wear, your metabolism, and even your level of hydration.
If you choose to go with a natural down sleeping bag (How do you decide?), then you must familiarize yourself with the different classifications of down that are used in the market. When shopping for a sleeping bag you will often see a down “fill” rating, such as 800-fill, 700-fill, 600-fill, etc.
The “fill power” of down is a way to speak of the down fiber’s loft, or “fluffiness”, which equates to the effectiveness of the down’s insulation. The higher the fill power, the better the down will be at trapping air and thus insulating you from the elements. The higher quality down will also be lighter and more compressible than the lower quality down.
So, all other things being equal, a 20-degree sleeping bag with 800-fill down will be lighter and pack down smaller than a 20-degree sleeping bag with 600-fill down. The tradeoff, of course, is that the 800-fill sleeping bag will have a much higher price tag. This is one of the primary reasons that you will notice seemingly comparable sleeping bags may have price differences of several hundred dollars.
For example, let’s look at two sleeping bags that have nearly identical temperature ratings, but have dramatically different mass weights and prices – the 800-fill power Sierra Designs Cal 13 weighs 1lb 12oz, whereas the 700-power Zissou 12 from Sierra Designs weighs 2lb 7oz. It is also worthwhile to note that higher quality down isn’t the only way that manufacturers trim weight from their ultralight bags. Many of the lightest models feature shorter zippers, thinner shell materials, and simpler baffle designs. It all goes back to what I said previously… “lightweight, affordable, and durable is the ultimate trifecta, but unfortunately you usually can’t have all three at once.”
In Part I I mentioned that I chose a Sierra Designs Zissou 12, which is a 700-fill power, DriDown sleeping bag. I think that it is an excellent choice, with a great balance of price, weight, and performance. I have fielded questions from several readers for recommendations on a slightly cheaper option, and in that case I would look at the Kelty Ignite 20 (EN-rated at 16 degrees), which also features DriDown technology, and won the Outside Magazine 2013 Gear of the Year award.
I hope these posts will help you make an educated purchase in the future. As always, please let me know if you have any questions!