Evaporative Cooling 

• Evaporative cooling vests are typically submersed in water for around 3 – 5 minutes and lightly wrung out or blot dried. They are usually worn outside the clothing and as the water in the vest interacts with specially treated cooling crystals or other cooling agents and the water evaporates, body temperature is effectively reduced.
• Can be made of FR (Fire Retardant garments) as well such as NOMEX and INDURA, etc.
• Advantages of using the Evaporative Cooling garments are; They are a cheap alternative to the other cooling vests and products, Lightweight thus ideal of Sports such as Motocross, Fitness, Jogging, and or any other outdoor athletic or recreational activity that requires minimal garment weight.
• Disadvantages of using the Evaporative Cooling garments is that they completely stop working when Humidity rises to 80-85%. 
• Useful tip is to soak it in chilled water to give you this added cooling effect that will last longer.
• Below is a video and images of how the evaporative cooling vests work: