Have you ever shopped here? Checking out tartan fabric.

[Barb T]

Traditional tartan kilts are made from twill, a weave that produces a diagonal pattern in the weave by passing weft threads over two and under two, but offset by one thread from pick to pick. Plain weave is over one under one, the kind of weave that you see in standard shirt fabric. Twill produces a more "shape-able" fabric, which is useful for the kind of shaping and steaming used in kiltmaking.