37.5 Technology for Cycling Apparel – Winter Test

By Brandon Bilyeu

4 stars


It varies depending on the brand that uses the 37.5 technology.

Pactimo Summit Aero Mesh Top: $164

Pactimo Torrent Waterproof Jacket: $225

How is it obtained: review company samples

Website: 37.5 Technology , Summit Aero Mesh Jersey, Torrente waterproof jacket

RBR Sponsor: No

Tried: 25+ hours

Test Round #2

In summer 2022 I tested the 37.5 technology in a t-shirt and base layer and you can find the review. here. In short, I found that the kit with 37.5 technology seemed to stay drier and cooler in hot weather than a similar kit without 37.5. I've now had the opportunity to test a 37.5 kit in cold weather to see how it performs.

The next two sections contain the explanation of Technology 37.5 from the previous review. It's certainly an interesting thermal regulation concept with some evidence to back up the performance claims. Below these sections you can find my cold weather review.

37.5 Technology: What is it and how does it work?

37.5 Technology is a company that is not a clothing brand itself, but licenses its performance-enhancing materials to be used in all types of clothing. 37.5 technology is incorporated into garments ranging from sleepwear to workout clothes and everything in between. The list of cycling brands using 37.5 includes Ashmei, Trek, dhb, Katusha, Mavic, Mission Workshop, Pactimo and Rivelo.

According to 37.5, the ideal core body temperature for performance and comfort is 37.5 degrees Celsius and the ideal relative humidity at skin level is 37.5%. In simple terms, 37.5 technology is integrated into the clothing and helps with thermoregulation to keep you at the right temperature for better performance, whether you're cycling or sleeping. This is achieved with small active particles of volcanic sand embedded in the clothing material.

Special volcanic sand has two characteristics that lead to its thermoregulation ability. First, sand absorbs infrared (IR) light at the wavelength emitted by the human body. Second, sand has billions of micropores, which greatly increases the surface area compared to a solid piece of sand of the same size.

image credits Emilian Robert Vicol and @jupiterimages

Volcanic sand absorbs IR light emitted by the human body and is porous on a much smaller scale than the volcanic rock shown above.

Most bike kits are made from synthetic materials with moisture-wicking properties to draw liquid sweat away from our skin, promote evaporative cooling, and keep the material dry. But we don't start sweating until we're already hot. As the body warms, the microclimate of our skin changes from low humidity to high humidity and eventually liquid sweat is formed. Absorbent materials only begin to cool in the liquid phase, but 37.5 aims to begin to cool in the moisture phase.

Infrared absorption, maximized by the large surface area, is the "magic" that makes thermoregulation work. When the body is relatively cold, the particles absorb and retain IR radiation to help maintain heat. If the body is hot and generating sweat vapor, the active particles use IR energy to move additional moisture into the environment, providing a cooling effect. This cooling may be enough to completely prevent liquid sweat from forming, but if exertion levels are high enough, liquid sweat can still form and wet the material. In this case the moisture transfer no longer works.

With the presence of liquid, sweat evacuation and evaporative cooling now occur and particles also play a role here. The porosity of the particles distributes the liquid over a large surface area, which leads to faster evaporation. So, when 37.5 is integrated into an absorbent material, very effective evaporative cooling occurs and the material remains drier.

Laboratory tests show quite impressive figures

To achieve maximum athletic performance, the goal is to keep the body's core temperature low. Skin temperature is more a matter of comfort. The University of Colorado Boulder did an independent study with cyclists comparing three cases: a long-sleeve shirt with wicking technology, the same long-sleeve shirt but with 37.5 added, and a cooling vest with water circulating at 4 degrees Celsius (39 F). . In summary, the study found that test subjects were able to perform at high intensity up to 26% better with the 37.5 technology t-shirt compared to the wicking t-shirt. And the 37.5 performed similarly to the cooled vest. For those interested in more details, a summary of the study and results can be found. here.

While the lab test results of 37.5 are impressive and demonstrate that 37.5 isn't all marketing smoke and mirrors, the 26% likely won't transfer directly to the road. The only variable I don't see mentioned is airflow. Unlike walkers or runners, cyclists move quite quickly and airflow plays an important role in ventilation and evaporative cooling. The wicking shirt will perform much better with moving air and this could close some of the performance gap to 37.5. There is a good reason why we use six fans at a time when using the indoor trainer. This study in a static laboratory points to a good performance of 37.5 when climbing steep slopes, since the speeds, and therefore the airflow, are much slower.

Torrent waterproof jacket with 37.5 technology – Keeps rain and sweat away

First, a disclaimer: my body is not perfectly calibrated to measure external skin temperature or internal core temperature, so my 37.5 performance observations will be limited to perceived comfort on the bike in terms of temperature and dryness compared to my typical riding gear.

The Torrent Rain Jacket is a lightweight, waterproof jacket that fits snugly and packs away, but retains some functional features. The Torrent has two rear pockets made of mesh to store items that can withstand exposure to rain and a waterproof zippered side pocket large enough to hold a phone. The two-way front zipper means you can open it from the bottom to cool off while still getting superior rain protection. My only complaint is that the sleeve length is a little short, although cuffed gloves will fill the gap.

The Torrent's waterproof fabric is equipped with 37.5 technology which I found very effective in keeping me dry from both rain and sweat. Most of my tests were conducted at temperatures between 0 and 7°C (32 to 45°F), in both dry and rainy conditions. My bike trip was the perfect testing ground as I know exactly what to wear for each temperature and weather condition thanks to a lot of trial and error.

This allowed me to purposely overdress on the go with the Torrent to test the moisture management and I was impressed with the performance. Where I expected to be drenched in sweat by the end of my ride like I would with a normal rain coat, I was simply hot and humid. Of course, opening the front zipper is much more effective than 37.5 at dumping heat, but the Torrent doesn't have vents, so your arms and back still rely primarily on 37.5 to keep things dry. When it rains, the ambient humidity is high, which hinders the 37.5's performance, but rain also has its own cooling effect.

Summit Aero Mesh Jersey with 37.5 Technology: Indoor Tested, Summer Ready

The name of the shirt sums up its design succinctly. It's a tight streamlined fit made from a lightweight mesh that's pretty sheer. On the back there are three standard pockets plus a zipper pocket. Intended for fast, hot days on the bike, I've been testing it on the indoor trainer since it's the middle of winter in the northern hemisphere. I used to wear t-shirts in the trainer, but I switched to nothing on top because I was hot and soaked even with three big fans running around at full speed. A great testing ground for a summer t-shirt.

The snug fit means the shirt acts as a wicking base layer as well as having 37.5 technology. For workouts from Zone 2 to the Sweet Spot, the shirt kept me relatively cool and dry (fans blaring, of course). More intense workouts overwhelmed the moisture transfer of 37.5 and liquid sweat formed. But the mesh construction of the shirt and the 37.5 porous surface area meant that evaporation was very effective in keeping the shirt reasonably dry and me at a bearable temperature. Before, with and without a jersey, there was enough liquid sweat for my torso to drip onto my bike. The Summit shirt at 37.5 never got wet enough to leak no matter how hard I tried.

Bottom line

Ride hard enough and sweat is inevitable, but the 37.5 technology seems to delay the onset of liquid sweat and then helps with evaporation when the sweat finally arrives. In both summer and winter testing I felt the benefits of having 37.5 Technolgy in my garments. Stopping or delaying the onset of liquid sweat is important in cold weather to avoid freezing, and the 37.5 technology certainly helps keep sweat at bay for more comfortable winter rides.

Brandon Bilyeu is an avid recreational roadie living in Regensburg, Germany. He travels by bicycle all year round and is a mechanical design engineer by profession. Click to read Brandon's full biography..

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