If you’ve ever bought outerwear made from down or other goose down products for winter weather camping, hiking, or snow sports, you’ve probably seen fill power ratings on the labeling.

What is down fill power though? And does it matter for keeping you warm? Read on to learn all about down fill power before you start the search for the best down jacket on the market. While fill power doesn’t measure warmth directly, it is an important factor in understanding how down garments work.

What fill power measures is the quality and efficiency of the down insulation. So it tells you how much down is required to capture heat. Together with the amount of down used in the garment, you can use this to figure out how warm it will be.

You can make a down comforter in an afternoon with basic sewing skills.

Fill Power Ratings 

If you’re on the hunt for the warmest outdoor wear you can find, understanding fill power is a big help. And let’s be honest, almost everyone is looking for as much warmth as they can get when getting ready for a winter hiking or camping trip. So let’s dig into fill power. Fill power, as mentioned above, measures down quality. More specifically, fill power measures the cubic inches of loft produced by an ounce of down.

Loft, in this case, refers to how “fluffy” the down is, or how much space it takes up. This is directly related to the amount of heat the down can capture. So a higher quality down with more “loft” will have a higher fill power and capture heat more efficiently. A lower quality down will have less “loft” and a lower fill power. 

With all this in mind, it starts to become clear what fill power is all about: efficiency. A higher fill power means a down jacket can be lighter and easier to store while being just as warm. So a 500 fill power jacket is not necessarily less warm than a 900 fill power jacket, it’s just that a jacket with a low fill power will need to be much bulkier to provide the same amount of warmth. 

What’s So Special About Goose Down

This all makes a bit more sense when you consider the mechanics of how goose down keeps you warm. There’s a reason, after all, that goose down is the insulator of choice for so many outdoor brands. The way that goose down works to keep you warm is by trapping pockets of warm air close to your body in between the feathers. The air trapped in these little down clusters keeps you warm.

This is the same way down keeps a goose warm and is the same mechanism that most synthetic insulation aims to imitate. While some of those synthetic alternatives can be better for wet weather or special applications, goose down remains one of the warmest, lightest, and most compressible options for cold weather. 

Now in most down fills, there’s a variation in the size of the feathers and how many of them are truly down versus slightly larger and bulkier feathers. Higher quality down is going to have very small/fine feathers and very few non-down feathers in the mix. So high quality down can keep you very warm and is also quite soft to the touch. 

This also depends somewhat on where the down was taken from. Goose down occurs in two basic varieties: natal down and body down. Some other birds also produce “powder down” which forms from the breakdown of larger feathers. With goose down, the important thing to know is that body down, the under plumage of mature geese, is generally considered to be higher quality than natal down, or down from goslings that haven’t matured yet. 

Kinds of Down 

Alternatives like duck down can be just as effective though, and Eider Duck down is even considered to be the finest down option of all. This is very expensive though and the duck is endangered in many places. So goose down remains the most popular option on the market as it provides almost the same level of quality.

Other types of duck down are also used, but some have a bit of a “gamey” smell compared to the fresher smell of cleaned goose down. Most goose down is referred to as “white” goose down, but the color of goose down doesn’t actually matter that much.

While the soft, fine down used for insulation is white most of the time, it can turn gray or brown in the summer months. It may not look as nice as white down, but it works just as well if it’s still from the downy under-layer of feathers. 

The Down Fill Power Test 

Now that we’ve looked at what fill power means and how it indicates the quality of goose down, we can look at the full fill power range available as well as how down’s fill power number is determined. As we now know, high fill power indicates higher quality down that provides more heat capture per gram of down. So let’s look at how this number is determined.

A higher fill power indicates more down clusters and larger clusters per gram. These larger clusters trap more warm air, making it easier to keep toasty. So how do you find out how many clusters there are and how much air is trapped? In a fill power test, goose down is placed in a plexiglass cylinder and then compressed until all the air is removed. The more air is captured, the less space the down will take up when compressed.

So better quality down is more compressible than lower quality goose down and will take up less space after a down fill power test. In a standard down fill power test, 30 grams of down is used in the compression, and environmental factors like temperature, humidity, and other influences must be accounted for. Fill power numbers range from 550 to over 800, and anything over 650 is considered good quality, with fills over 800 being the highest quality. 

What Is Fill Weight?

Once the fill power of the down is determined, there’s one other measurement to consider: fill weight. With both fill power and fill weight in mind, you can figure out exactly how warm, light and compressible a down garment will be.  

We already know that higher fill power indicates greater efficiency and quality of the down, but what is fill weight? It’s pretty simple, this is just the weight of the down used in ounces. So a jacket with 100 grams of 450-fill-power down should be about the same warmth as a 900-fill-power jacket with 50 grams of down. 

Of course, this all depends a bit on how the down is distributed as well. Good quality down products will use baffles to distribute the down evenly and prevent it from bunching up at certain points. So, while fill weight and fill power are important considerations in finding the right down jacket for your needs, there’s a lot more to consider than just this!

Finding the Right Down Jacket

Finding the right down jacket for your next backpacking trip, camping expedition or day hike depends a lot on the amount of warmth you need. The best down jacket for climbers in very cold and unforgiving regions may need to aim for the maximum loft and warmth they can get. If you don’t need so much warmth though, a lighter option will be more comfortable. 

So you should balance warmth with weight and compressibility to fit your specific needs. You should also consider how long you’ll be out, how often you plan to use the jacket, and what other outerwear you’re going to have on or available. 

One final thing to keep in mind is the weather. Down gets heavy and pretty useless when it’s wet. This is one reason some people prefer synthetic insulation instead. But there are lots of ways to approach the problem. 

Some just use a waterproof shell to protect a down parka underneath, and really layering garments like this is the best way to stay warm and dry. It can be tempting to look for the one jacket that does everything, but nothing beats effective layering. After all, there’s very little that can beat the warmth-to-weight ratio of down insulation. 

The Responsible Down Standard

Down isn’t perfect though. Like any other product, there are more and less ethical ways to buy down products. So in addition to looking out for fill weight, fill power, and how the baffles are laid out, you should check your down products for Responsible Down Standard certification. This certification means that the down used did not come from animals subjected to unnecessary harm or cruelty.

Presented by the Textile Exchange, a global nonprofit for standards in the fibers and materials industry, this certification ensures that ducks, geese, and other down-providing animals are treated humanely. The group works with farmers, producers, and retailers to encourage the humane treatment of animals while producing down goods and to promote the welfare of down-producing animals. 

This certification has gained traction in part as a response to the prevalence of live-plucking and other inhumane practices reported by watchdogs in the industry. This issue is complicated by the fact that some geese and ducks are not used for just one product. So some geese are used to produce multiple products and it can be difficult to track which were used for what. 

The Responsible Down Standard certification has taken some of the guesswork out for consumers, however. So if you’re concerned about animal well-being and want to make sure the down your purchase was ethically produced, just look out for this certification.

There are other certifications you might want to look into for sustainability or labor practices, but at least on the sustainability front, down is often a much better option than the synthetic insulators offered as an alternative. 

More About Down: Comforters, Sleeping Bags, and Duvets 

And goose down is great for more than just jackets! In fact, some of the best cold-weather sleeping bags, duvets, comforters, and other products use down to provide warmth without too much weight. Just like with outerwear, down sleeping bags and bedding have the advantage of compressing quite a lot to take up little space in your pack.

In fact, some of the highest quality winter sleeping systems out there take up such a minuscule amount of space that they’ve allowed today’s ultralight backpackers and trekkers to go longer, farther, and faster than ever before. At the center of this technology, however, is the tried and true standard of winter wear: goose down. 

In addition to being considered the best option for outerwear, goose down is used in bedding so often because it can be very comfortable and light. In fact, one of the most common uses of high fill-power goose down is to make comforters that are warm without being too heavy.

Of course, the alternative is also popular too: comforters with a low fill power that can feel heavy without being too warm. The takeaway is that there’s a lot that can down with goose down, especially when you understand fill power ratings. 

Alternatives to Goose Down 

Of course, you’ll also find a lot of synthetic insulation options for outerwear, sleeping bags, and more when you walk into a big camping chain like REI or Cabela’s. These synthetic options often promise to be lighter and sturdier than goose down, but there are few that really beat out the power of down when it comes to ultralight insulation. 

Many of these synthetic fills are made of polyester and cotton blends. While these do perform a bit better in wet weather than down, traditional down fills match and even exceed synthetic blends in lightness, compression, and warmth. Plus, down can be produced much more sustainably, and doesn’t rely on chemical processes that can be harmful to the environment. 

Layering a down garment with a hardshell jacket is a great way to deal with heavy rain.

What to Do About Rain?

If you’re worried about rain or snow, you can combine a down garment with a waterproof windbreaker or even a hardshell jacket to get more protection from the weather. One advantage of layering up and using multiple garments for staying warm is that you can be ready for any weather!

If it warms up a bit, you can go down to just the shell, and if it’s dry, you might only need your parka. All-in-one approaches to outerwear leave you stuck with everything on at once, which can be heavy and uncomfortable. The best option for a great winter trip is to go with a real goose down parka and combine it with a waterproof outer layer. 

Final Verdict 

So, for many, the intersection of effectiveness, sustainability, and comfort makes down a clear winner for staying warm on a winter camping trip. After all, down is biodegradable and so won’t add to the pile-up of synthetic materials in landfills across the world.

It’s also really really good at keeping you warm! And with a better understanding of fill power, fill weight, and how down is classified, you should be set to get the most out of your next down insulated piece of outerwear. 

Bonus video: Check out this video of a down fill-power test in action!