What is the difference between the rough endoplasmic reticulum and the smooth endoplasmic reticulum?

The rough endoplasmic reticulum (RER) has ribosomes bound to its surface, and it has a flattened-sac appearance. The RER is involved in packaging proteins to send to the Golgi apparatus. The smooth endoplasmic reticulum (SER) has no ribosomes on its surface and has a branched tubular structure. It is the site at which certain lipid molecules are synthesized and it plays a role in detoxification of certain hydrophobic molecules.