GEAR REVIEW: Patagonia Airshed Pullover (Windshirt)

By Will Rietveld

A windshirt is a wonderful hiking garment under the right conditions – cool, overcast, and windy. Any two of those factors together constitutes good windshirt conditions. And, indeed, a windshirt over a baselayer is often an ideal combination for hiking comfort, especially in the cool months and mountains.

Windshirt breathability isn’t talked about much. They are designed to resist wind, using tighly woven fabric, calendaring, and coatings as design features to provide the desired performance. With their new Airshed Pullover, Patagonia emphasizes the garment provides “a balance between wind protection and breathability”. Is that possible, and does it make a difference under hiking conditions?

The Patagonia Airshed Pullover (3.7 ounces, $119) “balances wind protection and breathability”. (Patagonia photo)

Specifications and Features

Manufacturer	Patagonia (www.patagonia.com)
Garment	Airshed Pullover
Weight	Mfr. Weight 3.7 oz; measured weight men’s Large 3.65 oz
Fabric	Body: 1.3-oz 20-denier 100% nylon mechanical stretch ripstop with a DWR finish. Hem and cuff panels: 4.2-oz 79% nylon/21% spandex jersey
Features	14 in zipper, 1 zippered chest pocket (converts to stuff sack), stand up collar, raglan sleeves, elastic cuffs and hem, stretch fabric. Trim fit.
MSRP	$119

Testing

I tested the Airshed Pullover over an 8 month period that spanned three seasons, and 19 outdoor trips in a wide range of conditions. Photo taken at Capitol Reef National Park, Utah.

The soft and stretchy fabric used in the Airshed Pullover is the same as the shell fabric on Patagonia’s Nano-Air insulated jackets, which are in a new category called “breathable insulation”.

It’s claimed to have a trim fit, but I find the fit to be typical for a size Large, which is my normal choice (I’m 6’ tall, 165 pounds, and 34” sleeve length). It has enough room inside to fit over a thick baselayer or fleece top, and the sleeve length is spot on. For me, an excellent fit.

I read an earlier review of this pullover on a prominent lightweight backpacking website, that cited air permeability numbers for the Airshed Pullover in the 50 to 60 CFM range versus only 1 to 7 CFM for a conventional windshirt. Those numbers were obtained by the author from a manufacturer representative, and are not specifications normally provided by the manufacturers. The article boosted my expectations for the Airshed Pullover.

A quick fabric air permeability test can be done by putting your mouth to the fabric and sucking air through it. Applying that test, I found that the Patagonia Airshed Pullover has distinctly higher air permeability than the Montbell Tachyon Jacket (1.6 ounces) I used for comparison.

In my field testing I gathered some comparative data for the two garments by placing a Kestrel Model 4000 Weather Tracker inside the zippered garment and recording temperature and relative humidity at 10 second intervals during a 90 minute hike over undulating terrain. The garments were tested in early morning on cloudy days. The starting temperature inside the garments differed by about 10 degrees, and the starting inside RH differed by about 6 percent.

 

The temperature data show the inside temperature initially cooled as I started hiking in cooler air, then became fairly steady through the remainder of the hike. Adjusted for the initial temperature difference, the two garments maintained about the same inside temperature during the hike.

Relative humidity inside the Airshed Pullover increased during the first half of the hike, to a higher level than the Tachyon, then remained fairly steady at about 60 percent. RH inside the Tachyon increased slowly and modestly in the first third of the hike, then gradually declined. The data suggest that the Airshed Pullover held more water vapor inside, rather than exhaust it through the fabric.

These results are contrary to the air permeability numbers and my mouth test, which indicated that the Airshed Pullover should have better breathability and exhaust moisture vapor more readily. So why didn’t the Airshed Pullover perform better in my instrumented field test?

Discussion

It’s important to note that I did not feel much difference in comfort between the two garments during my testing. Furthermore, in all the product testing I have done over the years, I have never found that fabric breathability alone has much of an effect on perceived comfort. A much bigger factor, by orders of magnitude, is ventilation – simply open the front zipper and exhaust the steam. It’s much easier, and reliable, to adjust the front zipper for thermoregulation. Fabric breathability is minor compared to ventilation.

But there’s a wild card in this windshirt equation, and it’s called the sun. The radiant heat from the sun trumps everything, including opening the front zipper. If the wind subsides while hiking on a sunny day, a windshirt gets too hot inside and it has to come off. A windshirt works great in the sun on a windy ridge or constantly windy conditions, but in variable conditions the windshirt is on and off repeatedly. The best conditions for a windshirt are constant cool, overcast, and windy.

The key points in this discussion are:

·         Ventilation is much more important for garment comfort than fabric breathability.

·         Weather conditions have a larger effect on garment comfort than ventilation.

Assessment

The Patagonia Airshed Pullover is a very nice windshirt, but don’t expect its breathability claim to be a silver bullet. It’s an analogous situation to Gore-Tex; Gore-Tex first needs to be waterproof, then it provides breathability (not much). Similarly the Airshed needs to be wind resistant, then provide some breathability (not much). During my many outings wearing the Airshed, I looked for extended comfort while hiking after the wind stopped and the sun came out, and didn’t find any. It got too hot to wear and I had to take it off, just like any other windshirt.

My recommendation is to select a windshirt that has a full height front zipper so you can open the zipper as needed for thermoregulation. My personal preference is an ultralight windshirt, like the Montbell Tachyon Jacket (1.6 ounces), so it’s a no-brainer to keep it in your pack. However, many hikers love the Patagonia windshirts because of their excellent fit and light jacket feel. Whatever you choose, get one with a full height zipper, and don’t get enamored by fabric breathability because there is not enough there to make a difference.