What Is Down Fill Power (2026): Fill Weight, Synthetics

UPDATE February 2026: We’ve added a new section on the care of down and some notes on Outdoor Vital’s Zero Stitch fabric.

What does down fill power tell you?

The higher the filling power, the greater the loft. Down puffer jackets and sleeping bags keep you warm by trapping heat from your body in air pockets between the down. Higher down fill power means the down has more loft, which means more air pockets, which means more warmth is retained. If everything else is equal, this means that a garment with a higher fill power will be warmer than a garment with a lower fill power.

Unfortunately, all other things are never equal. Fill power alone is not enough information to know how hot something will be. There is no direct relationship between fill strength and how warm a product will keep you, as there are many other factors to consider, such as how much fill is in the product, how well it can expand within baffles or bottom chambers, how well the fabric blocks wind, and so on.

To know how warm a down jacket, sleeping bag or comforter will be, you need to know at least one other number: fill weight.

What is down fill weight?

Photograph: Tatiana/Getty Images

Down fill weight is a simple number. This is the amount of down in the product, usually measured in ounces or grams. Using down fill weight and down fill power together can give you a way to compare the two items. For example, the relative ability of a puffer jacket to retain warmth can be estimated by multiplying the fill power by the fill weight. This means that a 900 fill power jacket with a 2 ounce fill weight will be able to hold the same amount of heat as a 600 fill power jacket with a 3 ounce fill weight. The big difference between them, and the reason for their different prices, is the weight and packed size of each.

In jackets, the weight difference is not very big. That’s why some of our favorite puffer jackets have 600 fill power. However, when it comes to sleeping bags, things are different. Since sleeping bags hold a lot more stuff, the weight difference between equivalent amounts of fill power is more significant. Unless your budget is unlimited, you’ll want to pay attention to the heat-to-weight ratio. How much heat do you need, and how much weight do you mind carrying?

One downside to losing weight is that some manufacturers don’t list it. It’s great to call your puffer jacket 900 fill power down, but when you have to list that it only holds 2 ounces, it seems less impressive. Less reputable companies often do not advertise fill weight. We list the weight of all the jackets we test.

Other Factors to Consider

Courtesy of REI

While down fill power and down fill weight together give us a way to compare items, there are other things to consider to get an idea of ​​overall warmth. The third major factor is the baffles, which are compartments built into the product. If you sewed a piece of nylon into a shell and pushed it down a bit, gravity and momentum will push it down near the hem within a few minutes. To avoid this, textile manufacturers add baffles to keep the down in place. Baffle type and size play a big role in how warm your jacket, sleeping bag, or comforter will be.