The doublet is a garment, worn by both men and women from at least the end of the middle ages until about the 1700s. A variation of the garment can be seen today in the Indian Sherwani, a tight fitting across the breast jacket, that is usually coat length. It reaches to about knee-length, and like some doublets, buttons down the front.
Most doublets fit snugly over the body, providing a padded look, and feature the row of center buttons down the front, or alternately, the doublet could be securely tied with laces or pinned to produce the snug fit. There’s some speculation on what inspired the European doublet. Given the vast number of similar garments in the Middle East, it’s thought the style which first began in Spain, may have been just one of the cultural “loans” occurring after the Crusades.
Initially, men wore the doublet as protection under various kinds of armor. The doublet would fit tightly to the body and was quilted to prevent mail shirts (like the hauberk), or plate armor made of leather and metals (like the cuirass) from causing uncomfortable chafing. Early forms could be either hip length or short, depending upon whether they were to be worn under armor. As the doublet fashion trend grew, doublets were frequently worn on their own, and became more elaborate in style, and both men and women might wear them.
The earliest doublet styles often featured long skirts to hip length that ended in points. Lacking collars, these doublets were often called pourpoints. Collars for doublets did undergo changes through the next few centuries. A variety of collar styles each had their “day” in fashion history, including low collars, and very high ones especially as worn by aristocrats.
By the 16th century, the long-coated style was replaced by a short coat version, which could be worn with hose, often also lined and stuffed (bombasted). Some doublets began to feature peplums, short skirts that attached to the jacket at the waist, and padding became less fashionable. Sleeves of doublets underwent various changes. At first these were often loose, but it became more popular, especially as doublets were worn as outer clothing instead of under armor for sleeves to fight very tightly, and for them to feature lots of different decorations, like embroidery.
People of all classes might wear doublets. The wealthier folk in Europe choose expensive silks and fabrics, which usually were lined with material (if not also quilted) like linen. People in the middle classes would wear less expensive and less rare fabrics. Linen doublets, or even wool ones, were common for tradesmen and servants.