The word muslin is defined as a lightweight cotton in a plain weave. That is another way of saying cheap fabric. As a pattern maker, muslin is both a tool and a canvas. I use it to create patterns, and to test them out. I love doing a muslin fitting because I can draw on the garment using a sharpie and cut or tape fabric back together to change the fit or design at will. There is nothing precious about a muslin mock up; it is ephemeral, and can be treated irreverently. The muslin mock up is a test of my assumptions, measurements, and technique. The muslin mockup is a piece of visual communication with my client. It says "this is what I am planning to do with the design. Is this also what you want from the design?"