The Sasha Jr is a perfect short sleeve sun shirt for young riders. This training shirt features the 37.5® technology which is a patented thermoregulation technology has proven to help the body manage its core temperature. It keeps you comfortable by helping your body to maintain an optimum core temperature of 37.5° Celsius (99.5° Fahrenheit) which is ideal for peak athletic performance. The particles are naturally derived and work for the life of the product (it will never wash out!).