Lightweight Insulated Jackets for Backpacking: Weight, Warmth and Fill Power

Fill power is a loft measurement: how many cubic inches one ounce of down expands to fill under a standard test. 800-fill down lofts to 800 cubic inches per ounce, 900-fill to 900. It is a quality measure of the down itself, not a warmth rating of the jacket, and the four jackets in our catalogue prove the point on their own: the Rab Mythic Ultra uses 900-fill down and weighs 330 g (11.6 oz), while the Outdoor Research Helium Down uses 800-fill and weighs 275 g (9.7 oz). The higher fill power garment is 55 g heavier, because it is a different jacket with a different amount of down and different fabrics.

The number that would settle warmth arguments is fill weight in grams, and of these four makers only Patagonia addresses it — by stating that it is not published. Where the deciding figure is missing, this guide says so instead of ranking jackets by warmth, because any such ranking would be a guess dressed as a spec.

Buy the Outdoor Research Helium Down: 275 g (9.7 oz), 800-fill down, MSRP $279.00 — the lightest jacket in the catalogue and the lowest list price among the down options. It is the pack-and-forget camp layer for three-season trips.

Skip it if your trips are wet. Down loses loft when it gets damp, and loft is the entire mechanism, so for drizzle-prone shoulder seasons buy the Outdoor Research SuperStrand XT Hoodie instead: 318 g (11.2 oz), synthetic VerticalX ECO and SuperStrand insulation, hooded, MSRP $275.00. You pay 43 g for insulation that keeps working when the weather does its worst, at a list price $4.00 below the Helium's.

This guide will not rank these jackets by warmth: no jacket here carries a published temperature rating, and no fill weight is published for any of them. That is the industry's gap, not ours to paper over.

This is a specs comparison, not a test review — nobody wore these through a wet November to bring you a verdict. Every jacket here carries a verified retailer listing, and this guide lines up the published specs that exist for them: garment weight, insulation type, fill power where the maker states it, and manufacturer list price. Prices are list price only; weights are the manufacturer figures, converted at 1 g = 0.03527 oz.

The case against down in a wet climate is simple: down loses loft when damp, and a 34°F drizzle — the manufacturers' own care guidance says as much when they tell you to keep down dry — punishes it harder in practice than dry air well below freezing. Synthetic insulation loses less when damp and dries faster. The case for down is the weight column: the one synthetic here, the SuperStrand XT at 318 g, sits above the Helium Down at 275 g, and down's compressibility advantage in the pack is real.

The way I resolve it is by role, not material dogma. If the jacket lives in the pack and comes out at camp under a shelter, down's warmth-per-gram wins. If it will be worn while moving in damp weather, or under a shell in sleet where it picks up condensation, the synthetic is the piece with less to lose. The SuperStrand XT's build backs that role: Outdoor Research states it carries 15% more SuperStrand insulation in the torso than its LT sibling, which is a torso-warmth pitch for exactly that wear-it-moving use.

Outdoor Research Helium Down Jacket — 275 g (9.7 oz), 800-fill responsibly-sourced down, MSRP $279.00. The lightest and least expensive down option here, and the default pick for a camp puffy that disappears into a pack. Reason to skip: no published fill weight means its warmth class is unverifiable, and OR positions it as an alpine piece — if you want one jacket to wear around town and on trail, the Patagonia below is built for that double life.

Outdoor Research SuperStrand XT Hoodie — 318 g (11.2 oz), synthetic (VerticalX ECO + SuperStrand), hooded, MSRP $275.00. The lowest list price in the set and the only insulation here that shrugs off damp. Reason to skip: synthetic gives up compressibility — it packs bigger than either down piece near its weight — and if your climate is dry, you are paying the moisture premium in bulk for insurance you do not need.

Patagonia Down Sweater Hoody — 420 g (14.8 oz), 800-fill Responsible Down Standard down, 20D shell, hooded, MSRP $345.00. The heaviest jacket in the catalogue, and the one built to survive being worn constantly rather than stuffed and forgotten; Patagonia publishes the 20D shell denier, which nobody else in this set does, and states plainly that fill weight is not published. Reason to skip: 420 g is 145 g more than the Helium — if the jacket only comes out at camp, that is dead weight you carry all day.

Rab Mythic Ultra — 330 g (11.6 oz), 900-fill down, 10D Pertex Quantum recycled shell, MSRP $525.00. The highest fill power and the highest list price in the catalogue by $180.00. Reason to skip: without published fill weights you cannot verify what the $180.00 list price premium buys over the Helium, and its 10D shell is a fabric you baby. This is the connoisseur's pick, and the published numbers alone do not close its case.

Two of the four jackets here are hooded — the SuperStrand XT and the Down Sweater Hoody — and an insulated hood is a good trade for almost everyone: your head is a large uninsulated surface, and a hood works at camp when your hands are occupied. But note what cross-brand weight comparisons cannot tell you: published figures are not always quoted for the same size or basis, so treat small gaps between brands as noise and only trust weight deltas within one maker's line.

Shell denier — fabric thread thickness — is published for two of the four: Patagonia's 20D and Rab's 10D. Lower denier is lighter and more fragile; a 10D shell wants to live under a hardshell or above a campsite, not in the spruce. Where a maker does not publish denier, this guide does not assign one.

Is a 900-fill jacket warmer than an 800-fill jacket? Not necessarily. Fill power measures down quality — loft per ounce — not the amount of down in the garment. In this catalogue, the 900-fill Mythic Ultra weighs 55 g more than the 800-fill Helium, and without published fill weights, warmth cannot be ranked between them.

What temperature is each jacket rated to? None of them carries a published temperature rating, and this guide will not assign one. Any degree figure attached to a jacket in a buying guide is somebody's estimate; an earlier article on this site did exactly that, and it has been retired rather than repeated. Use weight, insulation type, and fill power as your comparison axes.

Down or synthetic for a wet climate? For a jacket worn while moving in damp cold, synthetic — the SuperStrand XT is the pick here. For a camp layer kept dry in the pack, down gives more warmth per gram. If you can only own one and your weather is honestly wet, buy the synthetic and stop worrying about it.

Are these prices what I will pay? They are manufacturer list prices only. RidgeNote runs no live price feed; follow the retailer link on each product page to see what a retailer is asking.