It is a characteristic of most indigo denim that only the warp threads are dyed, where as the weft threads remain plain white. As a result of the warp-faced twill weaving, one side of the textile then shows the blue warp threads and the other side shows the white weft threads. This is why blue jeans are white on the inside. The indigo dyeing process, in which the core of the warp threads remain white, creates denim’s fading characteristics, which are unique compared to every other textile.

Etymology and origin

The word “denim” comes from the name of a fabric that was first made in the city of Nîmes, France, by the André family. It was originally called serge de Nîmes but the name was soon shortened to “denim.”

Denim has been used in the United States since the late 18th century.

Denim was traditionally colored blue with indigo dye to make blue jeans, although “jean” formerly denoted a different, lighter, cotton fabric. The contemporary use of the word “jean” comes from the French word for Genoa, Italy (Gênes), where the first denim trousers were made.

The following table shows where the world’s denim mills are located.

Wikipedia