It might be cotton muslin, but I don't know if this is the traditional material.
Muslin is a very loosely woven material, but with thick threads. That means you can see through it when you hold it against the light, but it looks more substantial when no light is shining through.
Muslin is more like the name of a category of cloth, not the name of a specific cloth. Things like cheesecloth are called muslin, but are probably woven too loosely for your purpose. Things like nut milk bags are also called muslin, but are probably too fine. General information like weight per square meter won't help much either because a fabric might be heavier because it's either woven loosely from heavier thread or because it's woven tighter from finer thread.
I'm afraid you'll have to try samples from some different fabrics. A local fabric store will probably make this process much easier than ordering samples online.