Twill is a beautiful fabric. It is detailed and elaborate and comes in a variety of patterns and styles. Depending on the color of the threads used and the weave variation, it can produce a diagonal or herringbone texture. Twill fabrics are often more substantial (thicker) and less transparent than a broadcloth of similar quality. Twill fabrics will also usually be a bit more shiny, and drape in a way that is softer than broadcloth or pinpoint.
Within the twill fabric family, you can find a variety, including:
Imperial and Cavalry Twills
These are the thickest twills, and they will have a very bold, noticeable texture to them.
These have less diagonal texture than the Imperial or Cavalry Twills, but their texture will still be noticeable from a close distance. We typically reserve this name for very high thread count twills (120s) that are of only the best quality.
Woven more tightly, the diagonal texture will only be apparent on close inspection. A simple, solid color twill dress shirt is extremely dressy and fit for any formal occasion.
Believe it or not, denim is also a type of twill. Look closely at your jeans and you will see the fine diagonal texture.
Twill Fabric Weave
By varying the weave slightly, significantly different patterns can emerge. Here are two similar weaves that produce a diagonal texture:
A herringbone variation here: