The FFC to activated with water gel "with the function of both hot and cold" Excellent. Heat retention is high, skin friendly brushed covers included. Cover can take your microwave to warm the water activated gel express the warmth of your warm water gently. Be cool when you use it to storage in the freezer for the next event the coldness of the ice with a water activated gel allows you to communicate. Freeze and also soft fit for your body. When cold, warm, or as needed for a moderate heat while providing comfort. Use over and over again.