What Is Goose Down Fill Power? (2023): Fill Weight, Synthetics

The construction method also affects how much warmth a garment can retain. If something says it’s sewn through, it’s exactly what that sounds like. There are two layers of fabric sandwiched around the insulation, and it’s stitched into a square grid or elongated column pattern. In particularly cold weather, the parts of the material where the stitching runs can develop into cold spots.

Baffle box construction looks the same from the outside at first glance, but it has vertical walls between each box of insulation that run perpendicular to the face fabric. Because it’s warmer, baffled construction is typically reserved for more expensive jackets.

If all else is the same, an ounce of 800-fill down will keep you warmer than an ounce of 650-fill down, and it’ll compress to a smaller size, meaning you’ll have an easier time stowing it in a pocket or bag. Almost universally, higher-fill down will cost more, and once you get up to 800- to 1,000-fill power, you’ll be paying several hundred dollars for whatever you’re buying, whether it’s a technical outdoor parka, winter sleeping bag, or cozy bed comforter.

What About Synthetic Insulation?

Synthetic down substitutes, such as PrimaLoft, don’t use fill power as a measurement. That makes it harder to compare warmth between two jackets.

One approach would be to find out the weight of insulation in the garment, though manufacturers don’t always disclose this information. Even if you reach out to customer service to find the fill weight, the comparison is thrown off if the type of synthetic insulation differs from one garment to the next. PrimaLoft Gold is different from PrimaLoft Silver, which differs even more from 3M Featherless. There just isn’t an easy metric for comparing synthetic insulation, the way you can use down fill power for goose down.

Synthetic insulation doesn’t compress down as small as goose down, and it doesn’t yet match its warmth. To make a synthetic jacket as warm as a down jacket, the manufacturer has to stuff more insulation into it, making it bulkier and puffier. I buy goose down exclusively when working in temperatures below 30 degrees Fahrenheit.