Fat molecules are triglycerides, each containing a glycerol head attached to 3 fatty acid tails.

A fatty acid is a long chain of carbon and hydrogen atoms (hydrocarbon).

The nonpolar hydrocarbons are hydrophobic ("afraid" of water) and are insoluble in water.

The dense covalent bonds make fats ideal for long-term energy storage; many animals develop a taste for sweet and fatty foods.