Brown fat is specialized for the generation of heat (thermogenesis). In adult humans, it is found in small amounts in the upper chest and neck.
Brown adipocytes are smaller cells with a centrally located nucleus and many small lipid droplets (multilocular). The abundance of mitochondria accounts for the brown color characteristic of its gross appearance.
Brown adipocytes uniquely express uncoupling protein-1 (UCP-1) in their mitochondria. It uncouples oxidation of fatty acids by allowing an influx of protons into the matrix of mitochondria. This energy is dissipated as heat.
The differences between the much larger, unilocular white adipocytes and the smaller, multilocular brown adipocytes and can be easily seen in those areas where they are mixed together.