Placing phase changing materials into garments is a game changing strategy for agencies looking to keep their officers comfortable while the world around them is stifling. Phase changing materials (PCMs) are heat exchanging, space-age garments with the ability to reduce skin temperature and therefore core temperature. This technology is available now and companies have responded by making public safety specific products.
Having been an officer on patrol in the Central Valley in California, where summertime temperatures remain in triple digits for several days at a time, I learned strategies for keeping cool. The truth is, core temperature doesn’t just affect fatigue—it can affect an officer’s decision making.
Along with my fellow officers I donned a uniform in a good dark color, efficient in turning sunlight into radiating heat. I wore a good insulating vest, which assured every wearer a barrier from escaping sweat, and a good insulating layer that could keep the core temperature a little higher than the ambient temperature. On our most fortunate days, we responded to assist in vehicle collisions that would take us out of our cars, where we could enjoy the mid-day sun and that refreshing smell of cooking pavement.
Research has shown that the temperature of arterial blood entering the brain can reduce the number of muscle activation signals sent when an athlete’s core temperature rises. This is one of the reasons why pro cycling team members distribute “ice socks” for the jersey back pockets in warmer venues. The brain has to stay cool so it can run the rest of the body.
Various studies about core temperature and cognitive function suggest that decision-making is challenged as the body core temperature rises. For law enforcement officers, thermoregulation could be a matter of officer safety.
We have moved into an era of technological improvements in fabric for tactical garments.
When it comes to keeping officers cool in uniform, the past few years have shown significant product improvements.
If you have been on the range lately on a hot day and the guy next to you was wearing a black polo, you have probably been introduced to coldblack technology, a product of Schoeller of Switzerland.
The coldblack finish allows dark color garments to reflect the infrared from sunlight. Not only does this offer UV protection, but it reduces heat buildup near the skin. Coldblack is a textile finish that reduces UVA and UVB absorption, which lowers heat buildup on the wearer. Garment giants like Under Armour Inc. offer coldblack in several of their athletic products. Vertx is another, and it looks pretty good over a vest. Their’s is a 6.5-ounce, 100 percent polyester shirt that allows for full range of motion and body armor. The Vertx coldblack polo has features that make it ideal for active law enforcement assignments like bicycle patrol and special details. It feels good against the skin, breathes well, and has strategically placed gussets that allow for full firearms manipulations. It also has shoulder pen pockets and sunglass loops.
Other products use moisture wicking to provide moisture management and quick drying to keep the wearer cool.
Some companies have developed products that react with the differences in internal and external temperature and moisture. Shoeller Technology has a product that responds to the outside climate and levels of physical exertion. This product is a membrane which is permanently wind and waterproof. However, as the body’s temperature goes, the structure of the membrane opens to allow excess heat to escape. The membrane contracts during lower periods of activity. Therefore, it allows for better heat retention when the wearer is cold and better breathability under exertion. The membrane is a polymer structure called c-change.
The most interesting, and perhaps the most effective cooling innovation, is phase changing technology.
Phase change materials (PCMs) are materials that can absorb energy, then release them in the form of heat later on. During the time that this happens, the material changes its state. That is, when it absorbs heat, it generally goes from a solid material to a liquid material—a phase change. When a material releases heat, it goes from a liquid to a solid.
The PCM concept was originally developed for NASA. PCMs absorb, store, and release heat. A PCM is a material that changes its phase, usually from a solid to a liquid, as it absorbs heat. This description covers a lot of materials with plenty of property characteristics. Ideally, the change in phase happens right around the ideal operating temperature.
If you have ever seen those heating pads that look like a liquid enclosed in a thick plastic pouch with a small metal disc inside, you probably have been introduced to sodium acetate. The liquid inside is heated past the melting point of the crystals. Allowed to cool at room temperature, it stays somewhat “stable” until activated by pressing the metal disc. It immediately crystallizes, which is an exothermic (heat energy releasing) reaction. Thus, heat is released when it changes phases. This particular PCM is a reusable heat pack.
PCM technology is comparable to ice in a drink. That is, water is a PCM material. As it changes from solid to liquid, it absorbs heat and cools the drink, keeping that drink at the desired temperature for longer.
Outlast uses micro encapsulated PCMs, which they call Thermocules. Obviously, the trick to introducing PCMs into a garment is to have a PCM which changes phases over a very narrow margin, while staying permanently part of the garment.
In textiles, there are different ways of putting phase changing material into fabric. These PCMs are a little bit more efficient than water. There is also a very small temperature difference between the melting and crystallization point. In order to make them work in clothing, they have to have a large amount of thermal conductivity. That is, they have to be pretty efficient in changing the environment around them.
I definitely understand the science here. However, how they manage to permanently fuse a PCM material into a garment is beyond me. In some PCM products, the PCM itself is encapsulated in polymer spheres. Now think about this: in order for this to work, they can’t be altered by washing the garment. The PCM product has to be affixed to the material so that wearing, handling, and washing won’t change its quality. It still has to maintain all the other qualities of the fabric that made the garment desirable in the first place. That is, it has to stay colorfast, flexible, comfortable to wear, durable and easy to maintain.
It won’t do any good to talk about PCMs unless we can share personal experience with the products. So I went to 91 Degrees F, a manufacturer of public safety specific products, and tried them out.
91 Degrees F makes garments specifically for public safety and military users. They use Outlast technology in base layer shirts and shorts. The material is soft polyester that has a silky feel against the body and the fabric is sewn with flat seams to prevent chafing. The most noticeable part about the t-shirt design is the lack of the seam that runs down the center of the armpit in a conventional t-shirt.
Outlast, the product used in manufacturing 91 Degrees F garments, uses a coating on the textile itself. They are locked into the fibers, preventing any handling or washing from dislodging the coating.
We put the 91 Degrees F base layers to work, in uniform, in the Central Valley in California. Our testers remarked about the noticeable difference in heat reduction and build-up under the vest. We tested them for several months, washing the garments dozens of times. The 91 Degrees F compression shirts move with the body, and don’t bunch up under the vest. The fact that the shirts were comfy, barring any other factor, made it worth our while. The technology embedded in the product only made it better.
A lot of garment testing can be very subjective, so the 91 Degrees F base layers were also inspected with an infrared thermometer. Obviously, measuring the temperature of the garment wasn’t as critical as measuring the temperature of the skin in contact with the garment. 91 Degrees F derives its name from the temperature set point of human skin. The closer these garments can maintain the set point in warm temperatures, the more efficient the product. In a side-by-side comparison between 91 Degrees F garments and products of similar construction without the PCM quality, the difference was measurable.
The PCM materials in the 91 Degrees F garments also aid the user in colder environments. Because of the reduced sweating under a vest in cold weather, cold weather gear can do what it was designed to do.
Using PCM garments goes beyond just keeping the ambient body temperature stable. Under a uniform, there are areas that would be hot and other areas that could potentially cool quicker. PCM materials allow temperature stabilization in zone. They also will allow temperature changes by activity level and external environment.
There are plenty of traditional ways to keep cool in hot weather. For officers on patrol, check out space age technology.
Lindsey Bertomen has taught shooting techniques for over a decade, in addition to teaching criminal justice at Hartnell College in Salinas, California. Off the clock he enjoys competing in shooting sports, running and cycling events. He welcomes comments at [email protected].
