Figuring out ways to mitigate the risk of heat exhaustion is critical, and that includes dressing appropriately.

Japanese Researchers Experiment In June 2019
For the experiment Ichinose set nine mannequin torsos out in the Japanese summer sun, each clad in a different colored polo shirt, then after five minutes of exposure checked the fabrics’ surface temperatures.

As expected, the white shirt was the coolest, with a temperature of approximately 30 degrees Celsius (86 degrees Fahrenheit), more or less the same as the air temperature during the test, followed by YELLOW. The next coolest shirts, in order, were GREY and RED, the latter a surprise since RED is generally thought of as a “hot” color in terms of psychological effect.

PURPLE ended up right in the middle of the pack, with the next, BLUE, again being somewhat unexpected, since in visual design it’s considered a “cool” color. Next came GREEN, then DARK GREEN, and, finally, BLACK, with the last two both having surface temperatures of over 50 degrees Celsius (122 Fahrenheit), more than 50 percent hotter than the WHITE shirt.

This essentially meant that the WHITE shirt and the BLACK shirt had around 20 degrees Celsius difference in surface temperature!

The difference is actually due to what wavelengths of light the colours reflect and absorb, along with the heat energy associated with those wavelengths. WHITE reflects all wavelengths of light and its heat, while BLACK absorbs all wavelengths of light and its heat.

The next time you are sick of wearing WHITE on a hot day, you can consider wearing YELLOW, LIGHT GREY or RED, which have a relatively higher reflectance.