Fashion fads come and go, but denim jeans will always be a wardrobe essential for many people. It's the denim style that fluctuates year after year, with certain decades witnessing an increase in baggy jeans and others full of tight, low-rise moments. However, no matter what kind of jeans you wear, it's important to buy them in a good quality brand that will last you for several years. Denim is a term used to describe cloth made from cotton fibers treated with sodium hydroxide (caustic soda) to create a hard, durable fabric suitable for making pants. There are two main types of denim: dark and light. Dark denim is made from 100 percent cotton fibers while light denim usually contains some polyester fiber too. Both fabrics can be used to make blue jeans but because of its durability, colorfastness, and resistance to water and chemicals, true denim comes only from cotton. Synthetic materials such as nylon can be used instead but they don't fit like real denim clothes do and they look out of place with other clothing items. Blue jeans have been around since the 1940s but they weren't called "blue jeans" back then. The original jeans were brownish-gray and had patches of white cotton thread stitched onto the leg opening of each pocket.