A jacket’s fill power is the down’s quality and amount of loft. You’ll see jackets labeled as 600-fill or 800-fill, for instance. The fill weight, which is measured in ounces, reflects the density or amount of down stuffed inside the jacket.
So when two 700-fill jackets have different weights, we know the heavier one is warmer.
On the other hand, if two down jackets weigh the same with different fill power (two 15-ounce jackets with 650-fill and 800-fill), the higher fill jacket is going to be less bulky, lighter, and more compressible.
It’s tricky to compare jackets with differing fill power. But in general, the lower the fill power, the less loft and warmth.
The Rab Neutrino is one of the warmest jackets on our list with a high fill weight, but is consequently on the heavier side; (photo/Chris Carter)