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

Fill power is a loft measurement: how many cubic inches one ounce of that 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. Higher fill power means you need less weight of down to reach a given loft, and loft is what traps air and keeps you warm.

Here is the part most buying guides skip. Fill power tells you nothing about how much down is in the garment. A jacket stuffed with a lot of 800 fill can easily be warmer than a thin one built with 900 fill. The number that would settle it is fill weight in grams, and fill weight is not published for any jacket in this comparison. Neither is shell fabric weight, which also moves the total.

The data here proves the point on its own. The Rab Mythic Ultra uses 900 fill and weighs 330 g (11.64 oz). The Arc'teryx Cerium SL Hoody uses 850 fill and weighs 210 g (7.41 oz). The higher fill power garment is 120 g heavier, because it is a different jacket with different amounts of down and different fabrics. Treat fill power as one input, not a ranking.

This is a specs comparison, not a test review. Nobody wore these through a wet November in the Whites to bring you a verdict, and I am not going to describe a shivering night I did not have. What I did is line up the published specs that exist for these twelve jackets, garment weight, fill power, down or synthetic, hood or no hood, and manufacturer list price, and reason carefully about what those numbers do and do not tell you.

That is a real limitation and I would rather state it than paper over it. Fill weight, baffle construction, shell denier and down treatment are not in this data set, so this guide does not rank jackets by warmth. It ranks them by what is published. Prices are manufacturer list price only. Weights are the manufacturer figures, converted at 1 g = 0.03527 oz.

The case against down in the Northeast is straightforward. Down loses loft when it gets wet, and loft is the whole mechanism. A 34-degree drizzle at 3,000 feet is the condition that punishes down hardest, worse in practice than dry cold at much lower temperatures. Synthetic insulation loses less when damp and dries faster.

The case for down is the weight column. The two synthetics here, the Outdoor Research SuperStrand LT Hoodie at 320 g (11.29 oz) and the Arc'teryx Atom Hoody at 375 g (13.23 oz), sit with the heavier end of the hooded down jackets, not with the light end. The Mountain Hardwear Ghost Whisperer/2 Hoody is a hooded 800 fill down piece at 234 g (8.25 oz), 86 g less than the SuperStrand LT. Whether that gap represents equal warmth is exactly what I cannot tell you, because fill weight and synthetic loft weight are not published.

The way I resolve it is by role, not by material dogma. If the jacket lives in the pack and only comes out at camp under a shelter, down and its weight advantage make sense. If the jacket is going to be worn while moving in wet conditions, or worn under a shell in sleety weather where it will pick up condensation, synthetic is the less fragile choice and you pay for that in grams.

This set contains the cleanest possible test of that question, because Mountain Hardwear publishes both versions of the same jacket. The Ghost Whisperer/2 Jacket is 207 g (7.30 oz) with no hood at $340.00 list price. The Ghost Whisperer/2 Hoody is 234 g (8.25 oz) with a hood at $375.00 list price. Same 800 fill down, same family. The hood costs 27 g, under an ounce, and $35.00 of list price.

Twenty-seven grams for an insulated hood is a good trade for almost everyone. Your head is a large uninsulated surface, a hood works when you are sitting still at camp with your hands occupied, and it means a lighter hat can cover the rest. If you already sleep in a hooded bag and hike in a shell with a good hood, the case is weaker, but 27 g is not the reason to skip one.

A caution about comparing published weights across models. The Patagonia Down Sweater Hoody is listed at 371 g and the hoodless Down Sweater at 386 g, which puts the hooded version 15 g lighter. Published figures are not always quoted for the same size or the same specification basis, so a 15 g inversion between two models tells you the numbers are not directly comparable rather than that hoods reduce weight. Within one model family the comparison is trustworthy. Across brands it is not.

Three jackets sit under 240 g, and the spread between them is only 27 g. All three are 800 or 850 fill down. This is the weight class where a jacket disappears into a pack, and also where shell fabrics get thin enough that snagging becomes your problem, though shell specifications are not published in this set.

Mountain Hardwear Ghost Whisperer/2 Jacket, 207 g (7.30 oz), 800 fill, no hood, list price $340.00. It is the lightest item in this comparison. Reason to skip it: no hood, and at $340.00 list it is not inexpensive for a jacket you may need to supplement with headwear anyway.

Arc'teryx Cerium SL Hoody, 210 g (7.41 oz), 850 fill, hood, list price $380.00. The interesting fact here is that it carries a hood and still weighs 3 g more than the hoodless Ghost Whisperer/2 Jacket. On published specs this is the most weight-efficient hooded piece in the set. Reason to skip it: $380.00 list is the second-highest price here, and the SL designation signals a stripped-down build whose fabric weights and fill weight are not published, so you are trusting the brand rather than a number.

Mountain Hardwear Ghost Whisperer/2 Hoody, 234 g (8.25 oz), 800 fill, hood, list price $375.00. This is the middle answer for most backpackers: hooded, under 240 g, and from a family whose weight figures are internally consistent. Reason to skip it: it is 24 g heavier than the Cerium SL Hoody for $5.00 less list price and 50 fewer fill-power points.

Montbell Alpine Light Down Jacket, 255 g (8.99 oz), 800 fill, no hood, list price $239.00. This is the lowest list price of any down jacket in the comparison. For 48 g more than the Ghost Whisperer/2 Jacket it costs $101.00 less at list price, which is the clearest weight-versus-price trade in the set. Reason to skip it: no hood, and 255 g puts it above three hooded jackets here.

Arc'teryx Cerium Hoody, 280 g (9.88 oz), 850 fill, hood, list price $400.00. The heavier sibling of the SL: 70 g more jacket at the same fill power. Reason to skip it: $400.00 is the second-highest list price in this guide, and since fill weight is not published you cannot verify what those 70 g over the SL actually bought you.

Outdoor Research Helium Down Hoodie, 310 g (10.93 oz), 800 fill, hood, list price $329.00. Reason to skip it: 310 g is 76 g more than the Ghost Whisperer/2 Hoody at the same 800 fill for $46.00 less list price, and without published fill weights there is no way to confirm those grams are insulation rather than fabric.

Rab Mythic Ultra, 330 g (11.64 oz), 900 fill, hood, list price $525.00. The highest fill power and the highest list price here by $125.00. It is also 120 g heavier than the 850 fill Cerium SL Hoody, which is the single best illustration in this guide that fill power alone does not predict garment weight. Reason to skip it: $525.00 list is a lot to pay for a spec sheet that shows only fill power in its favor while showing 96 g more weight than the lightest hooded option.

Outdoor Research SuperStrand LT Hoodie, 320 g (11.29 oz), synthetic, hood, list price $229.00. It carries the lowest list price of anything in this comparison and is the lighter of the two synthetics. If your trips are wet shoulder-season New England and the jacket gets worn rather than stored, this is the profile that fits. Reason to skip it: 320 g is 86 g more than a hooded 800 fill down jacket here, and no fill power equivalent or loft weight is published for synthetic insulation, so it cannot be compared on the same axis as the down pieces.

Arc'teryx Atom Hoody, 375 g (13.23 oz), synthetic, hood, list price $300.00. It is the second heaviest jacket in the set. The Atom is built as a wear-while-moving piece rather than a stationary belay layer. Reason to skip it: at 375 g and $300.00 list, it is 55 g heavier and $71.00 more list than the SuperStrand LT with the same published insulation category.

The honest summary of the synthetic question: on published specs I can tell you the synthetics here weigh 320 g and 375 g, and that hooded down options in this set start at 234 g. I cannot tell you the warmth ratio, because no fill weights, loft figures or temperature ratings are published for any jacket in this comparison. Anyone who gives you that ratio without those numbers is guessing.

Patagonia Down Sweater Hoody, 371 g (13.09 oz), 800 fill, hood, list price $329.00. The Down Sweater line is the everyday jacket that also goes backpacking, and its weight reflects a build meant to survive being worn constantly rather than stuffed and forgotten. Reason to skip it: 371 g is 137 g more than the Ghost Whisperer/2 Hoody at the same 800 fill.

Patagonia Down Sweater, 386 g (13.61 oz), 800 fill, no hood, list price $279.00. Reason to skip it: it is the heaviest down jacket here and has no hood, which is the wrong end of both columns for a backpacking layer.

Rab Microlight Alpine, 445 g (15.69 oz), 700 fill, hood, list price $275.00. It is the heaviest jacket in the comparison and the only one using 700 fill. A lower fill power means more weight of down for the same loft, and this is the one jacket where the published weight and the published fill power line up as you would expect. Reason to skip it: 445 g is more than double the Ghost Whisperer/2 Jacket.

For most backpackers wanting a hooded down jacket, the useful range in this set is 210 g to 234 g: the Arc'teryx Cerium SL Hoody at 210 g and $380.00 list, or the Mountain Hardwear Ghost Whisperer/2 Hoody at 234 g and $375.00 list. If you skip the hood, the Ghost Whisperer/2 Jacket at 207 g is the lightest thing here, and the hood costs 27 g within that family, which is a trade I would take.

If list price is the binding constraint, the Montbell Alpine Light Down Jacket at $239.00 is the least expensive down option and the Outdoor Research SuperStrand LT Hoodie at $229.00 is the least expensive jacket overall and the one that handles wet cold with less to lose.

One last time, plainly: everything above comes from published manufacturer specifications compared against one another. There are no temperature ratings, no fill weights and no measured loft figures in this data, and where those are missing this guide says so instead of filling the gap.

Is a 900 fill jacket warmer than an 800 fill jacket? Not necessarily. Fill power measures how many cubic inches one ounce of down lofts to, so it describes down quality, not total insulation. Warmth depends on how much down is in the garment, and fill weight is not published for any jacket here. In this data the 900 fill Rab Mythic Ultra weighs 330 g while the 850 fill Cerium SL Hoody weighs 210 g.

Down or synthetic for wet, cold New England conditions? Down loses loft when wet and loft is what keeps you warm, so a 34-degree drizzle is harder on down than much colder dry air. Synthetic handles damp better and dries faster. The cost shows in the weight column: the two synthetics are 320 g and 375 g, while hooded 800 fill down options start at 234 g.

How much does a hood actually add? Within one model family you can measure it. Mountain Hardwear publishes the Ghost Whisperer/2 Jacket at 207 g without a hood and the Hoody at 234 g with one, so the hood is 27 g and $35.00 of list price. Across different brands the comparison breaks down.

What temperature is each of these jackets rated to? None of them carry a published temperature rating in this data set, and I am not going to assign one. Any degree figure attached to a jacket in a buying guide is almost always somebody's estimate. Use weight, fill power and insulation type as comparison axes instead.

Are these prices what I will pay? These are manufacturer list prices and nothing more. RidgeNote does not operate a live price feed, so nothing here reflects what a retailer is asking on any given day.