The adipose tissues are totally different from each other on a cellular level. White fat cells contain one large drop off fat each. Brown fat cells contain multiple fat droplets and a lot of mitochondria. You can se the difference in the image below.                 https://scienceisntscary.files.wordpress.com/2014/02/fat-cells.png They se also derived from different tissues, white fat is related to connective tissue and brown fat is related to muscle tissue.  As @googlygoink said, their jobs are different brown fat makes heat while white fat stores fat. So white fat just grow and grow and store more and more fat. Brown fat is burning fat and keeping us warm.  It's worth to mention that grown ups only have really small amounts of brown fat, and the tissue doesn't grow so it won't crush our organs.