Fill power is a loft measurement, not a temperature rating. A 550 jacket carrying 200 g of down is warmer than an 800 jacket carrying 90 g, and an 800 vest with sewn-through seams will still leave cold lines across your chest at -10°C. The short version: 550 to 700 covers almost every city winter, and 800 is worth the money when you need the same warmth at half the packed volume, not when you need more heat.
What 550, 700 and 800 actually measure
The test is old and boring. One ounce of down goes into a graduated cylinder, a weighted plate sits on top for a fixed settling time, and someone reads how many cubic inches the down springs back to. 550 fill recovers to 550 cubic inches per ounce, 700 to 700, 800 to 800. Larger, springier clusters trap more air per gram, and trapped air is the whole product.
Two labs running the same sample rarely agree to the digit. US and European methods use different cylinder diameters and settling times, and the spread on one batch of down commonly runs 30 to 50 points. A jacket labelled 700 in one factory measures 660 in another and 730 in a third. Treat the number as a band, not a grade. Anything sold as 800+ is usually 800 to 850 with a marketing round-up.
The blend underneath matters too. Decent down runs roughly 90% clusters and 10% feather; cheap down pushes feather toward 20% and collapses faster. I took apart a 2019 parka that started near a claimed 700 and measured closer to 600 after four winters in a stuff sack.
Where the number stops mattering
Fill weight is the other half of the equation and the half nobody prints on the hangtag. A short puffer carries somewhere between 90 g and 200 g of down; a long parka can run 250 g to 300 g. Adding 60 g of 550 does more for warmth than climbing from 550 to 800 at the same weight, because you are adding material instead of making the material more efficient.
Baffle construction decides whether that loft survives being worn. Sewn-through stitching pinches the down to almost nothing at every seam, so a jacket with channels every 8 cm has a thin cold line every 8 cm. Box-wall baffles hold full thickness but add bulk and cost. On a short city jacket over a sweater, sewn-through is fine. On a long parka for -15°C, the seams are exactly where you feel the cold. I went deeper on that trade-off in sewn-through vs box-wall baffles, and the arithmetic of grams versus loft is in fill power vs fill weight.
Shell fabric is the third variable: a 20-denier face holds heat, a 10-denier one loses more to convection, and two jackets with identical fill specs can differ by 3°C to 4°C purely on the outer cloth.
550 and 700 in real weather
550 is the workhorse grade. It is heavier per unit of warmth, slower to dry, and completely fine for anyone who spends the winter between a heated flat, a bus stop and an office. I wear a 550-weight long parka from about 5°C down to -6°C with a merino base layer and a shirt, and I stop noticing the cold at the point where my hands give out first. Below -8°C it stops being enough unless the wind is dead.
The shapes that suit this grade are the long, boxy ones with room for a layer: a Canada Goose men’s hooded down puffer, the Canada Goose black fur hood parka for the deeper cold, and for milder days the Canada Goose black boxy down vest over a hoodie. A vest at 135 is a 0°C to -4°C garment in my book, and it is the piece I reach for most in November.
700 is where most of the jackets on this site sit, and it is the sensible middle. The same warmth arrives with 25% to 30% less fill weight, so a hip-length jacket stops feeling like a duvet. My test window: -4°C to -12°C with a midlayer, and the cuffs and collar are usually what fail first, not the chest. On the Moncler Maya 70 hooded short down jacket the fill sits dense and even through the body, and the glossy shell cuts wind better than the shine suggests. The glossy black Moncler Parana puffer is the trimmer cut of the same idea, and it runs a full size small through the shoulders compared with the Maya.
Longer 700-weight pieces behave differently because length adds fill weight without adding loft. The Prada belted hooded long down jacket covers the thigh and traps a pocket of warm air there, which is worth more at -10°C than another 50 points of fill power would be. It also wrinkles across the lap when you sit, and the belt is ornamental rather than structural.
800 in real weather
800 is a weight-saving specification before it is a warmth specification. The gain over 700 is roughly 10% to 14% more loft per gram, which shows up as a jacket that packs to two thirds the size and weighs 150 g to 200 g less. For travel, or for anyone who walks fast and overheats, you feel that on your back by 4 p.m.
Where it goes wrong: 800 down needs a lighter shell to be worth anything, and a 10-denier face fabric punctures on a bus seat corner or a bike lock. I have a 12-denier 800 jacket with four patches on the sleeve from two winters of normal use. It also costs 30% to 50% more for warmth you cannot measure with a thermometer.
Inside a heavy parka, 800 is wasted money. The Canada Goose arctic puffer parka style of long coat gets its warmth from length and fill weight, and putting 800 in it would save maybe 80 g on a 1.6 kg garment. The place where the grade earns its price is a light layer you carry: the Prada light Re-Nylon hooded puffer at 228, or the Prada black padded Re-Nylon vest at 135, which goes into a tote and comes out creased but functional.
The ladder in one table
| Fill power | Typical fill weight | Comfortable in still air | Best use | Watch out |
|---|---|---|---|---|
| 550 | 150-250 g | 0°C to -6°C | Long parkas, daily commute | Heavy, slow to dry |
| 650-700 | 110-200 g | -4°C to -12°C | Short puffers, layering | Cold lines at sewn seams |
| 800 | 80-150 g | -4°C to -10°C | Packable midlayers, travel | Thin shell, high price |
Those temperature bands assume a base layer, no wind, and a hood you actually put up. Add 15 km/h of wind and subtract 3°C to 5°C from every row. Take away the base layer and subtract another 2°C.
How I would choose
Start from the coldest hour you will actually stand in, not the coldest number on a forecast. If that hour is a 12-minute walk at 07:30 in January, 550 in a long cut is enough and you will not baby it. If you are outside for two hours at a time in -10°C, take 700 and check the baffles before the fill number. If you fly twice a month and need one jacket for a plane seat, a hotel room and a 5°C platform, pay for 800 in a light shell and accept the patches.
Fit changes the maths more than people admit. I am 175 cm and 72 kg, and I take a medium in Moncler’s short cuts, a large in Prada’s belted long coat, and a small in the oversized boxy vests, because the same nominal size moves 4 cm to 6 cm at the chest between those three patterns. Squeeze the down and it stops trapping air, so a jacket that is tight across the back is a colder jacket no matter what the tag says. The Moncler Tibb down vest is the clearest example I own: true to size over a shirt, one size up if you want a hoodie under it.
If you are still narrowing shapes, the puffer jacket category sorts by cut, and the Canada Goose puffer collection is where the long, high-fill-weight coats live. For the colder end of the scale, my notes on matching a rating to a real winter are in how warm is warm enough. Buy the fill weight and the baffle pattern for your winter; the fill power number is the last thing to argue about.