By Brandon Bilyeu
Varies depending on brand using 37.5 Technology
Pactimo Summit Aero Mesh Jersey: $164
Pactimo Torrent Rain Jacket: $225
How obtained: review samples from company
RBR Sponsor: no
Tested: 25+ hours
Testing Round #2
In the summer of 2022 I tested 37.5 Technology in a jersey and baselayer and the review can be found here. To summarize, I found that the kit with 37.5 Technology did seem to stay drier and cooler in hot weather than similar kit without 37.5. Now I’ve had the chance to test some 37.5 kit in cold weather to see how it performs.
The following two sections contain the 37.5 Techology explanation from the previous review. It’s certainly an interesting thermal regulation concept with some testing 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 an apparel brand itself, but licenses its performance enhancing materials to be used in all types of clothing. The 37.5 technology is incorporated in garments ranging from sleepwear to exercise and everything in between. The list of cycling brands using 37.5 include 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 Celsius and ideal skin level relative humidity is 37.5%. In simple terms, 37.5 technology is integrated into clothing and helps with thermoregulation to help keep you at the correct temperature for best performance, whether riding a bike or sleeping. This is achieved with tiny active particles of volcanic sand imbedded into the clothing material.
The special volcanic sand has two features that lead to its thermoregulation abilities. First, the sand absorbs infrared (IR) light in the wavelength that the human body emits. Second, the sand has billions of micropores which massively increases the surface area compared to a solid piece of sand of the same size.
The volcanic sand absorbs the IR light emitted by the human body and is porous on a much smaller scale than the volcanic rock shown above.
The majority of bike kit is made from synthetic materials with moisture wicking properties to move liquid sweat away from our skin to promote evaporative cooling and keep the material dry. But we don’t start sweating until we are already hot. As the body heats up our skin microclimate goes from low humidity, to high humidity, and then finally liquid sweat forms. Wicking materials only begin cooling in the liquid phase, but 37.5 aims to begin cooling in the humidity phase.
The IR absorption, maximized by the large surface area, is the ‘magic’ that makes the thermoregulation work. When the body is relatively cool the particles absorb and retain the IR radiation to help keep you warm. If the body is warm and generating sweat vapor the active particles use the IR energy to move the extra humidity to the ambient environment which provides 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 out the material. In this case the humidity transfer no longer works.
With the presence of liquid sweat wicking and evaporative cooling now take place and the particles play a role here too. The porosity of the particles spreads the liquid over a large surface area, and this leads to faster evaporation. So, when 37.5 is integrated into a wicking material it leads to very effective evaporative cooling and the material stays drier.
Lab Testing Yields Some Pretty Impressive Numbers
For maximum athletic performance the goal is to keep the body core temperature down. Skin temperature is more of a comfort issue. The University of Colorado Boulder did an independent study with cyclists comparing three cases: long sleeve shirt with wicking technology, same long sleeve shirt but with 37.5 added, and a cooling vest with water circulating at 4 Celsius (39 F). In short, the study found that the test subjects were able to perform at high intensity up to 26% longer with the 37.5 technology shirt versus the wicking shirt. And the 37.5 performed similar to the cooled vest. For those interested in more details a summary of the study and results can be found here.
While the 37.5 lab test results are impressive and prove that 37.5 is not just marketing smoke and mirrors, 26% likely does not transfer directly to the road. The one variable I don’t see mentioned is airflow. Unlike walkers or runners, cyclists move quite fast and airflow plays a big part in venting and evaporative cooling. The wicking shirt will work much better with moving air and this could close some of the performance gap to 37.5. There is a good reason we use six fans at once when riding the indoor trainer. This study in a static lab does point to good 37.5 performance when climbing steep grades as speeds, and thus air flow, are much slower.
Torrent Rain Jacket with 37.5 Technology – Keeps Away the Rain and Sweat
First, a disclaimer: My body is not perfectly calibrated to measure external skin or internal core temperatures so my observations of 37.5 performance will be limited to perceived comfort on the bike in terms of temperature and dryness as compared to my typical riding kit.
The Torrent Rain Jacket is a lightweight, waterproof shell that is trim fit and packable, but retains some functional features. The Torrent has two rear pockets made of mesh to store items that can handle exposure to rain and one zippered waterproof side pocket big enough to hold a phone. The two-way front zipper means you can unzip from the bottom to cool off while still getting upper rain protection. My only complaint is that the sleeve length is just a little short, though gloves with cuffs will fill the gap.
The Torrent’s waterproof fabric is equipped with 37.5 Technolgy that I found very effective at keeping me dry both from rain and sweat. Most of my testing took place at temperatures between 0 – 7C (32-45F) in both dry and rainy conditions. My bike commute was the perfect testing ground as I know exactly what to wear for every temperature and weather condition based on lots of trial and error.
This allowed me to purposely overdress on commutes with the Torrent to test moisture management and I was impressed with the performance. Where I expected to be drenched with sweat by the end of my commute as I would with a normal rain shell, I was just hot and humid. Of course, opening the front zipper is much more effective than 37.5 at dumping heat, but the Torrent has no vents so the arms and back still rely mostly on 37.5 to keep things dry. During rain the ambient humidity is high which hinders 37.5 performance, but rain also has its own cooling effect.
Summit Aero Mesh Jersey with 37.5 Technology – Tested Indoors, Ready for Summer
The jersey name sums up its design succinctly. It’s a skintight aero fit made from a lightweight mesh that is quite see through. At the back are three standard pockets plus one zippered pocket. Meant for fast and hot days on the bike, I’ve been testing it on the indoor trainer due to the fact it is the middle of winter in the Northern Hemisphere. I used to wear jerseys on the trainer, but I switched to nothing on top due to being hot and sopping wet even with three big fans running full blast. So, a great testing ground for a summer jersey.
The skintight fit means the jersey acts like a wicking baselayer in addition to having 37.5 Technology. For Zone 2 up to Sweet Spot workouts the jersey kept me relatively cool and dry (fans blasting of course). More intense workouts overwhelmed the 37.5 humidity transfer and liquid sweat formed. But the mesh jersey construction and 37.5 porous surface area meant that evaporation was very effective at keeping the jersey reasonably dry and me at a bearable temperature. Previously, with and without a jersey, there was enough liquid sweat for my torso to drip onto my bike. The Summit jersey with 37.5 never got wet enough to drip no matter how hard I tried.
Ride hard enough and sweat is inevitable, but 37.5 Technology seems to delay the onset of liquid sweat and then help with evaporation when the sweat finally arrives. In both summer and now winter testing I felt benefits from having 37.5 Technolgy in my garments. Stopping or delaying the onset of liquid sweat is important in cold weather so you don’t freeze, and 37.5 Technology certainly helps keep sweat at bay for more comfortable winter rides.
Brandon Bilyeu is an avid recreational roadie who lives in Regensburg, Germany. He’s a year-round bike commuter and is a mechanical design engineer by trade. Click to read Brandon’s full bio.