Muslin is an open weave fabric that has many uses. Muslin should be washed before use for straining as it it still has starch in it. Doublecloth is two fine muslin layers joined together, with a square woven pattern. We also have pre-made Muslin cloths.
Voile is similar but tighter woven from fine yarn, more floaty, used for fashion, craft and drapery. Also see Batiste, which is still very fine but not quite so sheer.