The application of both heat and cold is useful to relieve muscle or joint discomfort.
Warm/cool bag will help you to relieve pain in a localized and natural way. It is also useful for headaches or fever. The cold will provide you with analgesic and anti-inflammatory properties, while the heat will relax and promote blood circulation.
You can comfortably heat this bag in the microwave or cool it in the fridge freezer.