Duffel coats derive their name from the material from which they are constructed. The materiel, duffel, originated in Belgium and is a rather rough woolen fabric known for its thickness and insulation properties.
There are several properties of the duffel coat that distinguish it from other similar styles of coats; particularly felt coats. Most importantly the coat must be made from duffel and be approximately 3/4 length. Additionally duffel coats should have a hood, large covered pockets on either side and be closed with four large rope style fasteners placed evenly down the front.
The duffel coat first became popular during World War I and World War II when it was extensively used by the British Navy. Post-World War II a surplus of available coats caused their price to drop drastically and thus became popular among civilians. The duffel coat is still somewhat popular today, especially in European countries; though it is not nearly as popular as it once was.