Scientist know that like other cells in the body, each fat cell (Adipocytes) has a cell membrane and a nucleus, but their bulk is made up of droplets of stored triglycerides, each of which consists of three fatty-acid molecules attached to a single glycerol molecule. There are three kinds of fat, "white fat," which is the main substance used for energy storage. There are also "brown fat" cells,that produce heat, making brown adipose tissue pretty important for maintaining body temperature. Lastly, there is "beige fat," which is found in white adipose tissue, but unlike white-fat cells, these cells contain UCP-1. Beige-fat cells seem to have the flexibility to act like either white fat or brown fat, depending on the situation, according to the Endocrine Connections paper.