How do cooling shorts work (and do they?)?
There are many "cooling" fabrics on the market and each one works to cool your body a little differently. According to Jim Ross, SVP of product development at the American Textile Company, cooling technologies are separated into two categories, temperature balance and temperature abatement.
Generally speaking, cooling occurs when sweat evaporates from the fabric. It cools you down as the air moves through the material. "Breathable" fabrics tend to be more cooling. Fabrics like Nike's Dri-FIT, Adidas Climacool, and Undersummers. In these cases it is all about boosting evaporation.
The other technology is temperature, abatement which works by transferring heat. In this case, are fabrics where the temperature of the fabric is cooler to the touch than other fibers, providing a cooling sensation. Cool touch fabrics, often shown by language keeping you up to one degree cooler.When moisture is trapped and airflow occurs, it provides a cooling sensation with the airflow. Keep in mind, once a garment is on your body, the temperature of the fabric will adjust to your body temperature.
Do these products really work? In theory they should all work. There is one factor that can affect how cool you feel. This is how many barriers are between you and the textile. In the case of Undersummers, there is no barrier so the fabric should nicely move heat away from your body. Cooling fabrics keep all the time as you wear them because they are designed to perform when your body ads heat and moisture. They won't work when your body isn't there to notice.