Fat cells. Coloured scanning electron micrograph (SEM) of joined fat-storing cells (adipocytes). Fat cells are one of the largest cell types in the human body, each cell being 100 to 120 microns in diameter. Almost the entire volume of an individual fat cell consists of a single lipid (fat or oil) droplet. Fat cells and their supporting connective tissue (surrounding the fat cells), make up fat tissue. Fat tissue forms an insulating layer under the skin, storing energy in the form of fat created from excess food. Magnification when printed at 10cm wide: x 60