On the evening of October 9, 2025, Imogen Reece arrived at a small estancia outside Cochrane, in the Aysén region of southern Chile, with four insulated jackets folded into a duffel bag. She had agreed to wear them, in rotation, across two field seasons of work on a sea-bird recovery project in the fjords north of Caleta Tortel.
She came off the project on April 30, 2026. She had logged three hundred and eight nights of use across the four jackets. Two of them were down. Two were synthetic. The results, at the end, were not the clean victory for either material that the gear press tends to claim.
The jackets were a Rab Neutrino Pro 800-fill down, an Arc'teryx Cerium Lightweight 850-fill down, a Patagonia DAS Light synthetic with Plumafill, and a Rab Photon Pro with Stratus synthetic insulation.
The brief was unromantic. Reece would wear the jackets at camp, in the boat, on early-morning bird counts, and at the small kitchen where the project crew ate dinner. She would log warmth, compressibility, moisture handling, smell, and a category she called does it still loft at the end of each month.
The down jackets, on first wear, were the obvious winners on warmth per gram. The Rab Neutrino Pro, at 510 grams in her size, kept her warm at minus 4C with only a light fleece beneath. The Cerium, at 295 grams, was a thinner garment but still warmer for its weight than either synthetic.
By the end of the first month, in the wet maritime climate of the fjords, the down jackets had begun to behave differently. The Cerium, with its lighter fabric and less robust DWR, wet out at the shoulders during a six-hour boat ride in steady rain on November 12. The down clumped. The jacket's warmth dropped sharply. It took twenty-four hours in a dry kitchen to recover its loft.
This is not a defect of the jacket. It is a defect of using a light down jacket in a saltwater maritime environment. The Cerium is honest about its design brief. Reece used it after that day only inside the cabin and on dry trips.
The Rab Neutrino Pro, with a heavier face fabric and a hydrophobic down treatment, held up better. On a similar boat ride in mid-December the jacket showed beading at the shoulders for the first three hours and partial wet-out by the fourth. By morning, after a night on a hanger, the loft had recovered.
The synthetic jackets, predictably, were the right tool for wet days. The Patagonia DAS Light, on the same December boat ride, was damp on the outside and warm on the inside throughout. The Photon Pro behaved similarly. Neither lost loft when wet, although both became heavier and slower to dry than dry down would have been.
On warmth per gram, dry, the down jackets won by a clear margin. The Cerium provided roughly the warmth of the DAS Light at half the weight. The Neutrino Pro provided more warmth than either synthetic at a similar weight.
On warmth per gram, wet, the synthetics won by a clear margin. The Cerium became almost useless. The Neutrino Pro lost roughly a third of its warmth. The synthetics lost perhaps ten percent.
On long-term loft, after three hundred nights of use including frequent stuffing into a small pack, the down jackets recovered well. The Cerium lofted at the end of the project to perhaps 92 percent of its original thickness. The Neutrino was closer to 95. The synthetics, by contrast, had compressed perceptibly. The DAS Light had lost roughly twenty percent of its original loft. The Photon Pro had lost more.
On smell, no one talks about this in the gear press, but synthetics absorb body odour faster than down does and release it more slowly. By the end of the field season the synthetic jackets had a faint, persistent smell that washing in cold water did not entirely remove. The down jackets did not.
On price, the down jackets are more expensive. The Cerium is roughly 400 dollars at full retail. The Neutrino Pro is roughly 425. The DAS Light is 329. The Photon Pro is 285. Over a five-year lifespan the down jackets are likely the better value because they retain loft longer.
On ethical concerns, the down jackets in this test were both Responsible Down Standard certified. Reece will note, without arguing the larger question, that there is no equivalent certification of comparable rigour for synthetic insulation, which is a petroleum product with its own supply-chain implications.
What this all means is something the marketing copy on either side will not. In a dry cold climate, down is the right material. In a wet cold climate, synthetic is the right material for active days and down with a heavier face fabric is the right material for camp.
For most temperate-mountain users, one jacket of each type is the honest answer. For users who can only carry one, the answer depends on whether their weather is most often wet or most often dry. The Patagonian fjords are wet. A user in the Sierra Nevada at the same elevation would face a different question.
Reece has kept, for her own use, the Rab Neutrino Pro and the Patagonia DAS Light. The Cerium has gone back to a friend who wears it in the dry Colorado winter and is delighted with it. The Photon Pro is in a closet, awaiting the next field season, where it will earn its keep again. The right tool, after three hundred nights, is still and always the one that suits the conditions, and the conditions have a great deal to say about the answer.
