How to Compare Down Jackets | Beyond the Fill Power Number

Comparing down jackets means weighing fill power, fill weight, total weight, construction, and weather resistance — not just the fill power figure.

Most shoppers grab the jacket with the biggest fill power number, but that single metric only tells you how efficiently down lofts, not how warm the jacket will be. Two jackets with identical 800-fill down can differ dramatically in warmth when one packs in more ounces of down than the other. The key to comparing down jackets is checking five numbers and features together, then matching them to the conditions where you’ll actually wear it.

What Fill Power Actually Tells You

Fill power measures loft quality — how many cubic inches one ounce of down occupies. An 800-fill ounce fills 800 cubic inches; a 550-fill ounce fills only 550. Higher fill power means better insulating efficiency per ounce, which is why premium jackets use it to shave weight.

That efficiency does not translate to more total warmth. RAB’s buying guide notes that a jacket with less down at high fill power can be less warm than one with more down at lower fill power. The number describes the down, not the jacket.

Fill Weight and Total Weight: The Warmth Numbers

Fill weight is the actual ounces of down stuffed inside, and it’s the closest thing to a warmth spec you’ll find. Two 800-fill jackets — one with 6 ounces of down and one with 3.5 — are not in the same warmth class, even though the fill power matches exactly. Compare jackets at the same fill power first, then check fill weight to see which runs warmer.

When fill weight isn’t published, total garment weight is a rough stand-in. A heavier jacket usually means more insulation, but not always — shell fabric, zippers, and features add weight too. The most useful comparison is warmth-to-weight: how much warmth each ounce of jacket buys you. That’s why an ultralight backcountry piece like the Crazy Levity, at just 6.1 ounces total, is designed for moving fast in cold, dry conditions rather than standing around in town.

Construction, Weather Resistance, and Fit

Construction details matter as much as the down itself. Sewn-through baffles let cold air reach the inner layer at the stitch lines but keep weight low; box baffles trap more warmth at a weight penalty. A proper hood, adjustable cuffs, a hem drawcord, and wind-resistant fabric all change how warm the jacket feels in practice.

Down has one hard limit: it stops insulating when wet, which is why REI recommends down for cold, dry environments and synthetic insulation for cold, wet conditions or high-output activities where you’ll sweat heavily. If rain or wet snow is on the menu, a synthetic jacket or a down piece with a waterproof shell is the smarter call.

Fit changes everything too — a too-large jacket lets warm air escape at the wrists and waist, while a trim cut traps heat closer to the body and layers better under a shell. Reviewers consistently flag fit as a top factor in perceived warmth, so order from a retailer with an easy return policy if you’re between sizes.

Price and Real-World Value

Down jackets range from budget to expedition-priced, and cost tracks fill power, fill weight, and shell fabric more than brand. Eddie Bauer’s Stratustherm runs $150 with 650-fill down; the Cotopaxi Fuego costs $300 with 800-fill; Arc’teryx’s Cerium Hoody sits at $400 with 850-fill. The warmer, lighter, or more packable the jacket, the more it costs — but the best value is the one that fits your use case, not the one with the highest specs.

For a solid mix of warmth, weight, and price, the REI Co-op Magma 850 and Cotopaxi Fuego are staff-picked standouts. If you’re shopping on a tighter budget, our tested roundup of the best budget down jackets breaks down which affordable options actually deliver warmth for the money.

Check the manufacturer’s page for each jacket’s current specs before buying, since fill weights shift between versions and seasons. And remember that no spec sheet replaces trying the jacket on — expert testers at REI’s insulated outerwear guidance stress that real-world warmth depends heavily on fit, activity level, and layering underneath. The warmest jacket on paper is the one that fits you properly and matches the conditions you actually face.