A Crazy Idea That Worked

We humans are warm-blooded creatures. Mostly, this is a blessing. Because we produce our own body heat, we can venture out in almost any climate, day or night—there’s no bad weather, only the wrong clothes, as the adage goes. Unlike lizards, which must seek out any external source of warmth to keep their blood flowing, we can bang out some jumping jacks or snuggle up in a shiver bivy if we’ve blown our daylight or weather window. We might risk death, but never torpor.

Being endothermic can be a curse, however, when you start pushing yourself while bundled up. The heat you’re generating can’t make its way through the layers you’ve piled on to stave off the cold. As your heart rate rises, you start to sweat. If you stop and your sweat doesn’t dry, your internal temperature will free-fall; if you keep going, you’ll produce enough sweat that your body heat can’t keep it from freezing. The same regulatory system that allows us to run ultras in the desert will, in the wrong conditions, take you from sous vide to popsicle. Per Alpine Ambassador Dane Steadman, “Staying dry is the best way to stay warm in cold mountains.”

This is why moisture management is the foundation of cold-weather layering, and why technical fleece has been core to traditional mountain layering systems for decades. Fleece is warm and soft and can be made of fast-drying fibers woven into structures that wick moisture away from the skin. Yet, even the most futuristic fleece is relatively heavy from a gram-counting perspective, and heavier still when it’s soaked with sweat. The only way to lighten it up is to loosen the structure, making it airier, and therefore more air-permeable and chillier. In mountain environments, where you’re up in the clouds and up against rock, fleece needs a more protective partner.

Or does it? At Patagonia, you may have noticed, we’re proud of our contrarian minimalism. Who says we need two layers when we can do it with one? What if we made an insulating piece that traps heat but could be paired with more open, more breathable materials like a traditional woven jacket? When we first started exploring this, our suppliers thought we’d lost the plot.

“I remember trying to talk to them about the need for insulation that can be put into a breathable materials package,” says Kristin Umscheid, senior material developer. “They’d say, ‘That’s ridiculous, insulation is supposed to keep you warm.’ They couldn’t understand the need.”

For athletes pushing themselves in cold conditions, the need was obvious. How to achieve this functionality, however, was not. The same light, fluffy qualities that allow down feathers or synthetic insulation to trap heat come with a challenge: They like to bunch and move around. To solve this, these fibers are typically paired with a nonwoven material called a scrim. The scrim holds them in place, like feathers in a plastic bag, between a tightly woven liner and face fabric, like that slick nylon we all know and love. Those fibers aren’t going anywhere, but neither will your body heat. The second you start moving around too much, things start to get sweaty, fast.

For decades, there was no clear solution. Without the stability of nonwoven fabrics, the insulating fibers clump at the bottom of whatever they’re sewn into, or they wriggle out through permeable materials. “When you have an airy, open-faced fabric, the fibers sneak out,” says Maggie Elder, senior technical product designer. “So you need a material that’s stable enough that it doesn’t come out of the face fabric.”

Rather than give up, though, the designers in the Forge, as Patagonia calls its R&D lab, kept pressing for a solution. “Part of the reason I came here was that I was so impressed that we have all these internal methods and ancient methods to learn from and build off,” Kristin says. “Other brands will pick one insulation supplier, buy off the shelf and trust they’ll hit all the specs they need. Besides their field-testing, they don’t have the lab test methods to vet stuff out properly. No other brand is testing insulation like we are. We’re pushing the boundaries and coming up with new internal standards even for ourselves.”

The first proving ground for our crazy idea came along in 2014. With our textile partners, we had co-developed FullRange® insulation, a type of synthetic insulation that was light and stable enough to pair with more open fabrics, and we were ready to use it in a new layer for our mountain communities: the Nano-Air, the first of what is now its own category of technical clothing, “active insulation.” This is the Goldilocks of layering, with the compressibility and high warmth-to-weight ratio of insulation paired with stretchy, breathable and quick-drying woven fabrics. From the first time you try it on, you feel the difference; and, chances are, by the first time you start really jamming in it in cold weather, you’ll be a convert.

“Being able to do all of these high-output activities with a 60-gram midlayer on was mind-blowing,” remembers our Alpine Ambassador Anne Gilbert Chase. She’s been on the field-testing side of this process since the beginning. “We could wear this really warm but breathable midlayer all on its own in the mountains and not get soaked.”

Even though the first Nano-Air represented a breakthrough, it still ran hot. Insulation is measured by grams per square foot, and generally, the heavier the insulation, the warmer it is. “When we made the very first Nano-Air, the FullRange insulation had to be in the 60-gram to 80-gram realm to be stable,” Maggie says. “When I’m truly moving and exerting myself, this is still too warm. I need it to be lighter, more packable.”

Since then, Maggie and Kristin have pushed the materials further, trying lighter and lighter insulations, and even making a hybrid Nano-Air by adding fleece to the back and side panels. This was a bit of a bust and only lasted a few years. Knit fabrics are more breathable but also heavier, hold moisture for longer and don’t pack down as much, resulting in the dreaded “chilly back” when taking off your pack in windy weather after working up a sweat. “We were solving air-permeability, but were also dragging it down in other qualities,” Maggie says. Anne Gilbert agrees: “It just did not work as well.”

As we continued to explore what breathable insulation could be, other brands started to pick it up, too—at least in theory. By now, most of our competitors have an active insulation layer in their line. But more than half of them simply don’t let air through, reports Maggie, totally missing the magic of the material.

Maggie and Kristin know this because they can quantify air-permeability in the Forge with a machine that measures the cubic feet per minute of air pushed through a square foot of ­material (CFM/ft²). Our CFM machine (the FX 3300 by Advanced Testing Instruments, for those in the market) reads air-permeability on a spectrum of roughly 1,300 to 0 CFM, or from “mesh” to “plastic bag.” They spent the last several years dissecting other brands’ active insulation pieces and were surprised to find that, despite their billing, the overall materials package was not breathable. Most were essentially lighter-weight versions of traditional insulation—warm, compressible and much too close to 0 CFM for comfort.

“It’s proof that it’s hard to understand and test this,” Maggie says. “Some brands were using a regular insulation and choosing a soft-shell material that doesn’t have movement or breathability. Maybe they didn’t understand what that means for comfort. Not all the brands have the same resources we do here to test things on the spot for CFM. It’s hard to see what that is until you’re really hands-on with it.”

That hands-on access is what allowed Kristin and Maggie to take breathable insulation the furthest yet with the Nano-Air® Ultralight in 2025, the lightest active insulation piece currently available. There was only one textile mill that would work with us to develop this weight, a small family-owned Austrian company that Kristin calls “the best insulation factory I’ve ever seen.” They were willing to experiment and create the first 20-gram insulation layer that could hold up to our field-testers. For 2026, they’ve managed a 40-gram Nano-Air Light that’s more versatile and even more finely tuned.

“We were using the same face fabric and liner for most of our active insulation because we knew it worked. But for the new Nano-Air layers, instead of talking about ‘the materials package,’ we thought about it as components,” Maggie says. Rather than taking the average ratings for CFM, weight or warmth across the entire jacket, the team tuned each individual material to excel at its role in the garment. This had never been done before at Patagonia, let alone anywhere else.

“We found that when you start heating up, you want the thing that’s closer to your body to move air through faster. So we have a higher CFM liner, which pushes heat into the insulation quicker, and then a lower CFM on the outer to block wind and hold that heat in,” Maggie explains.

The result is jackets that are more comfortable next-to-skin thanks to the lighter liner and micro-texture that resists sticking when you sweat, and are more resistant to all the usual suspects in the field: precipitation, abrasion, snagging. Like the development process itself, each component sounds a little too niche to matter; but taken together, these layers have changed the game. “Even in early versions, the testers would refuse to send their protos back,” Kristin says, a good sign. Since then, the Nano-Air Ultralight has won over most of our mountain ambassadors. Timmy O’Neill memorably gushes that it’s “like wearing my own skin.” Jenny Abegg says that it “is seriously the most well-used and well-loved piece of gear I’ve ever worn.” True to form, Anne Gilbert says simply, “It works well.”

On his latest trip to Torres del Paine, Chile, Tommy Caldwell wore his continuously while he and his climbing partner Siebe Vanhee sent the 30-pitch South African Route in a day. “I don’t think I’ve taken this thing off since I got here,” Tommy says. “I wear it all day everywhere for every pitch and around town.” (Colin Haley, arguably our most obsessed layer strategist says that he is “staying open-minded to potentially preferring the Nano-Air.”)

The product team isn’t resting on its laurels; all these breakthroughs in Nano-Air have opened up a realm of possibilities for an entirely new layering paradigm. Insulated baselayers? Shell-less alpine climbing? Everything is on the table. But for now, Maggie is pleased. “It’s not often you can get intense athletes to change, especially those who have been in the game for a long time,” she reflects. “It’s satisfying to hear from them that the new Nano-Air allows them to eliminate some layers or to hear them say, ‘This is with me for every trip.’”