To eliminate future problems , get a compression micrometer to take to the fabric store. There's many kinds of good cotton material for patching , but w/o a way to measure true thickness , you could be wasting your time. Precut patches in commercial plastic bags , are mostly mislabeled as to thickness. .018 mics out to .014 , .015 at .012 , etc.. Get a mic . to take to the fabric store.