600, 650, 700, 800, 900... You'll find these numbers on almost every down jacket and sleeping bag label. Is the highest number the best? Not necessarily. At Plein Air Entrepôt, it's a question we hear all the time. Here's what that number really means, and what you should look at instead.
This number doesn't measure warmth
First thing to know: this number is the down's fill power. It isn't a measure of warmth. 800 fill down isn't automatically warmer than 650 fill down.
In fact, we have 650 fill down sleeping bags in store that are much warmer than some 800 fill bags. So right away, we can drop the idea that a higher number means a warmer product.
What fill power actually measures
Fill power tells you how much space, in cubic inches, one ounce of down (about 28 grams) takes up. The higher the number, the more the down lofts for the same weight.
In practical terms, higher fill power means:
- Lighter for the same amount of insulation.
- More compressible once packed in your bag.
That's it. Unless you're climbing Everest and counting every gram, the difference in fill power between two down jackets won't change much in everyday use.
Criterion #1: baffles
Baffles are the seams that divide the jacket into compartments. Their job is to keep the down in place so it doesn't shift around inside the garment.
When down migrates, empty spots form, and that's where you get cold. Some baffles are far better designed than others, and that's often what sets a great jacket apart from an ordinary one.
Criterion #2: fill amount
The second criterion is how much down is inside. You need a lot of it. If there isn't enough, even the loftiest down in the world will leave cold spots.
Our tip to check: hold your down jacket up to a light. If you often see light shining through, those areas are short on down.
A great example: the Mountain Hardwear StretchDown
Mountain Hardwear does something really smart with the StretchDown, its most popular jacket. Its baffles are built in a special way: slightly discontinuous and stretchy.
- The down stays put: no empty spots under the arms or across the shoulders, where other jackets often leave you cold.
- Incredibly comfortable: the stretch fabric moves with your body.
Summary
| Criterion | What it tells you | Impact on warmth |
|---|---|---|
| Fill power (600 to 900) | Volume of one ounce of down: lightness and compressibility | Low, except for ultralight use |
| Baffles | How well the down stays in place | Very high |
| Fill amount | How much down is in the garment | Very high |
The secret to a great down jacket isn't fill power: it's how the jacket is built, its baffles and its fill. Now you know. See you outside!
At Plein Air Entrepôt, we offer a carefully selected range of down jackets and sleeping bags from the best brands - Mountain Hardwear, Marmot, Outdoor Research and more - at up to 60% off regular prices.
Our team of outdoor enthusiasts is here to help you choose the best-built down jacket or sleeping bag for your adventures, based on your goals and budget.
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Plein Air Entrepôt - Trekking, hiking and travel specialists since 2007. Expert advice and warehouse prices.