Have you ever sewed a real masterpiece? Maybe a tailored blouse or blazert? Then you’ve probably sewn a muslin to check the fit of the pattern. It is time-consuming process, but it is worth it.
For this kind of test run you don’t need an extremely high-quality fabric, that’s for sure. Ideally, the material should be of the same weight and touch as the ‘good’ fabric that will be used later. Usually a simple Calico is sufficient. (Calico is a variation of the name of an Indian city where the material typically came from in earlier centuries.) ‘Our’ muslin fabric is made of unbleached cotton.
By the way: It is called ‘muslin’ as the main fabric used for it is usually a gauze fabric (in French: la mousseline).