Down vs Synthetic Insulated Jackets (2026)

Down and synthetic insulation both trap still air; they differ in what happens when they get wet and how much they weigh for the warmth. Down is lighter and packs smaller. Synthetic keeps working when it is damp. The specs that tell you which jacket is warmer are fill power and, more importantly, fill weight, and most listings give only the first.

How we chose: we did not test these jackets; we compared fill power, fill weight, shell and insulation specs from the makers' pages and listings, and kept only jackets sold by Amazon.com, the brand's store or Backcountry and in stock on September 29, 2026.

Six insulated jackets side by side

Prices are Amazon's, as of the time shown, and subject to change. Details

Rab's figures come from its product pages for the Microlight Alpine and the Neutrino Pro. The others are from the Amazon listings.

Fill power is quality, fill weight is quantity

Fill power is a volume. The testing lab IDFL describes it as the volume a set amount of down occupies under a set weight, reported in cubic inches per ounce. On IDFL's down testing page, common values run from 300 to 900, and "the greater the volume, the better the down will insulate."

So 800-fill down lofts more per ounce than 650-fill. That does not make an 800-fill jacket warmer than a 650-fill one. Rab puts it plainly: "Fill power is all about quality, not quantity."

Quantity is fill weight: how many grams of down are in the jacket. Rab publishes it. The Microlight Alpine holds 152 g of 700-fill; the Neutrino Pro holds 212 g of 800-fill. The Neutrino Pro has more down and higher-fill down, so on paper it is clearly the warmer jacket.

Columbia's listing for the Delta Ridge II gives 650 fill and no fill weight. Without that second number there is no way to rank its warmth against the Rab jackets from specs alone.

IDFL also notes that samples can be conditioned by several standardized methods before testing, so the same down can test at slightly different numbers. Treat a 50-point difference between brands as noise.

What happens when each gets wet

Down insulates by lofting. Soaked down clumps and loses that loft. That is why makers now treat it. Rab's listings describe Grangers hydrophobic finishes on both its down jackets and say the Microlight Alpine's treated down "traps body heat and dries quickly."

Read those claims for what they are: water resistance for the down inside the shell, not a waterproof jacket. Rab calls both shells water-resistant, not waterproof. In steady rain, a down jacket goes under a rain shell or stays in the pack.

Synthetic insulation is made of polyester fibers that do not absorb water the way down clusters do. Rab says the PrimaLoft Silver Rise in the Cirrus Flex "thrives in damp environments," and Columbia says its Thermarator insulation traps "warmth even when wet." Neither maker publishes a standardized wet-warmth test, so those are the makers' words, not numbers you can compare.

The practical rule: if the jacket will be damp from outside (wet snow, drizzle, a leaky tent) or from inside (sweat on a climb), choose synthetic. If the air is cold and dry and you need the most warmth for the least weight, choose down.

Which to buy

• Dry cold, hiking and camp: the Rab Microlight Alpine. Enough down for camp evenings, light enough to carry all day.
• Damp cold or hard effort: the Rab Cirrus Flex Hoody. Wear it on the move or under a shell.
• Everyday winter: the Columbia Delta Ridge II for dry days, the Powder Lite II for wet snow and sleet.
• Standing still in deep cold: the Rab Neutrino Pro. The most down here, and a hood that fits over a helmet.
• Hunting: the First Lite North Range. First Lite rates it for 20 to 45°F and built the pockets around a pack and bino harness.

Bottom line: buy one warm jacket for stops, not for moving. If you are sweating in it, it is the wrong layer for that part of the day; see our layering guide.

Patagonia and Arc'teryx make well-regarded down and synthetic jackets too, but neither sells them on Amazon through its own store, so they get no card here. Buy those from the maker.

Caring for down and synthetic

A dirty down jacket lofts less. Rab's down washing guide says to close the zips, turn the jacket inside out, wash it alone on a cool, long, gentle cycle with a non-biological or down-specific detergent, and air it for a couple of days afterward.

The same guide says to store a down jacket uncompressed in a cool, dry place. One left in its stuff sack all summer comes out flatter than it went in. Rab publishes a separate guide for synthetic jackets.

Cold, wind and hypothermia

An insulated jacket is only as good as the layers under it. Wind takes heat fast: the National Weather Service wind chill chart puts 5°F air in a 20 mph wind at a wind chill of -17°F. A windproof shell over the insulation keeps that wind out of the loft.

The CDC's hypothermia guidance recommends several layers of loose-fitting clothing and a water-resistant outer coat, and lists shivering, confusion, fumbling hands and slurred speech as warning signs. If you see them, get the person warm and dry and get medical help.

Related: merino vs synthetic base layers and mittens and gloves for extreme cold.

Frequently Asked Questions

Is 800-fill down always warmer than 650-fill?

No. An 800-fill jacket with little down can be cooler than a 650-fill jacket with a lot. IDFL measures fill power per unit of weight, so compare fill weight too, where the maker publishes it.

Can I wear a down jacket in the rain?

Only under a rain shell. Rab describes the Neutrino Pro's Pertex Quantum Pro shell as water-resistant, and hydrophobic down resists moisture but is not waterproof.

What does PrimaLoft Gold vs Silver mean?

They are PrimaLoft's grades. First Lite uses Gold at 133 g/m² in the North Range; Rab uses Silver Rise in the Cirrus Flex. The g/m² figure is the weight of insulation per square meter of fabric, so a higher number at the same grade is warmer.

Does an Omni-Heat lining make a jacket warmer?

Columbia says its metallic Omni-Heat lining reflects and retains body heat. It is a lining, not insulation: the down or synthetic fill still does most of the work.

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WildProofLab is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com. Fill power, fill weight and insulation specs are the makers' own.