Subcutaneous fat is the layer of subcutaneous tissue that is most widely distributed. It is composed of adipocytes, which are grouped together in lobules separated by connective tissue. The number of adipocytes varies among different areas of the body, while their size varies according to the body's nutritional state. It acts as padding and as an energy reserve, as well as providing some minor thermoregulation via insulation. Subcutaneous fat is found just beneath the skin, as opposed to visceral fat, which is found in the peritoneal cavity, and can be measured using body fat calipers to give a rough estimate of total body adiposity.