A key advantage of water is that its specific heat is very high compared with that of other mediums. For example, the amount of heat per unit mass required to raise the temperature of water by 1 ◦C is 4.186 J or 1 cal/(g ◦C) by definition. That of ice is 0.51 cal/(g ◦C), and of water vapor is 0.48 cal/(g ◦C) (at constant pressure). The specific heat of human tissue is 0.85 cal/(g ◦C) and that of air is 0.23 cal/(g ◦C)