Understanding Down Insulation

Understanding insulation, particularly down, is far more confusing than it should be, and it seems like the volumes of misinformation have been used to steer consumers in the wrong direction. For years I have helped customers crack the code to making the correct insulation selection. In my eyes, the insulation category includes jackets and vests, but crosses over into the sleep system category as well. There are all sorts of Synthetic options, but down is down, right? Not quite.

Chew on this: Down is graded by how much loft a single ounce yields (to get really specific, Americans use 28.4 grams, and European manufacturers use 30 grams) and the down rating you find or “fill power” is its lofted volume in Cubic Inches (with a weight placed atop it). The bottom line is, the numeric representation on down products relates to loft (read insulation) and that is we are paying for.

Unfortunately it isn’t so simple as reading the fill power rating. I want to try to make this more understandable from a practical standpoint. Let’s take in a few key facts first, then circle back to the fill power rating, and then I think you will have some practical knowledge to help you make a solid choice when it comes to down insulation.

First is temperature. All sleeping bags have a temperature rating, but few are actually correct. Hence the “buy a bag rated ten or twenty degrees cooler” rule of thumb. For years, many of us did this because the rating on the bags was somewhat arbitrary and many of us suffered through frigid nights as a result. EN ratings have come about over the last handful of years, and really cleaned up the process. While a bag may be called “20 degree super neeto sleeping bag,” opening it up would likely reveal that the comfort rating is only 45 degrees, and the extreme rating says twenty – meaning an early fall trip will likely be a little brisk. You may not die (unless it’s at your own hands) but you’ll certainly be miserable.

It will likely cost more to anti-up for a bag with a comfort rating in the realm you are looking for, but it’s no different than tires; you can buy a “mud and snow” tire for a Fiat, but you’d probably die of embarrassment if you put them on your hunting rig and got stuck on a wet cigarette butt. Get the appropriate bag for the job – if I anticipate 15 degree nights, and will be using a tent I will take a 5 to 10 degree bag and sleep as warm and cozy as a drunken baby. As a pretty good rule, tents will give you pretty close to an extra ten degrees of warmth but be cognizant of the fact that weather seldom accommodates our plans.

With Temperature addressed, we need to dig into weather. Down is a peculiar beast, what is perceived as the best down – 850 plus fill –is comprised of large “puffs” of down and has very little feather content. It is highly compressible, ways little, and a few ounces go a long way. However, it is extremely moisture sensitivity- if of those dainty little puffs get wet, you might as well be strutting around in or sleeping in a wet sleeping bag. This has been addressed from a few angles over the years, good textiles have proven really effective, as have waterproof stuff sacks; but recently we have seen hydrophobic down coatings make a big wave.

 In the context of moisture, we often think of rain, snow, or dew; but we can mitigate them by being attentive to how we handle down products. What most folks fail to consider is humidity, particularly that which the human body lets off as both water vapor and liquid moisture. These elements slowly degrade the loft your down over the course of a backcountry trip, diminishing down’s insulative values. As down dries, it comes back to life; but, but in mountain hunting we cannot expect unending sunshine.

 Hydrophobic coatings make down retain its loft longer, so when exposed to perspiration and exhaled water vapor the down retains its warmth longer. This is a big step. Now we need to circle back to ratings in the context of moisture, believe me, this step is where things start to come together.

Remember that little tuft of down? Within the down rating spectrum the tufts get larger as the number increase, so you get more insulation for a given amount of weight. However, The higher the rating of the down, the more responsive it is to liquid or vapor forms of moisture – 850 fill down will lose more loft after exposure to moisture than 700 will. In temperatures constantly below freezing, these effects are lessened and the volume of insulation needed often dictates high-loft fill down as the most effective solution.

Now we can add some new technology into the equation – hydrophobic coatings on the down itself. These coatings help mid-range down retain loft better when exposed to moisture, so you can get into insulation pieces that are still light and compressible, but the insulation variation from humidity is much less. This means, we get a sleeping bag that is consistently warm, even in a meteorological suck fest. 

This is where it turns into a value proposition. In conditions where above freezing temperatures will be expected, mid-range loft (600-750 fill) hydrophobic down offers greater utility and a lower price than ultra-premium down. The weight savings are tangible, as is the performance, if I had to choose a single bag to hunt the backcountry in the lower 48 this is the realm of bag I would be seeking. That said, there is no single perfect solution, but at least you now have the tools slice through the misinformation and BS that abounds in the down realm.