Outwardly, such jeans resemble cowboy trousers because they feature zippers in several locations, including the back of the legs, beginning at the buttocks and continuing to the bottom; the pockets; and the side seams of the legs. These factors started to decide the top spot amid the heaps of other garments. The word "denim" comes from the French dernier (last), which describes these pants because they were the last things made before starting on another season's clothes. In addition, these jeans were known as "work pants" because workers wore them while performing tasks outside over rough terrain. The need for durability led to various techniques being used to make the fabric more resistant to tears and stains. For example, buttons were replaced by snap closures, or rivets were used instead. Finally, these jeans are called "boy's jeans" because they were originally designed for men who worked on farms or in factories. They were often worn by young boys as well as adults to show their social status, especially after World War II when blue jeans became popular again. Nowadays, people usually refer to these types of jeans as "back-zip" or "front-zip". They are usually made out of cotton or polyester/cotton blends and can be white or black. Although they are most commonly seen around the world, there are some countries where it is not allowed to wear denim clothing, so they must be made of synthetics or wool.