We searched Medline and Embase, and used Google, including articles reporting the filtration properties of flat cloth, or cloth masks. We reviewed the reference lists of relevant articles and review articles, and identified articles the press. We found 25 articles. Study of protection for the wearer often used a manikin wearing a mask, with airflow to simulate different breathing rates. Studies of protection of the environment, also known as source control, used convenience samples of healthy volunteers. The design and execution of the studies was generally rigorously described. Many descriptions of cloth lacked the detail required for reproducibility; no study gave all the expected details of material, thread count, weave, and weight. Some of the homemade mask designs were reproducible. Successful masks were muslin at 100 threads per inch (TPI) in 3-4 layers (4-layer muslin or a muslin-flannel-muslin sandwich); tea towels (also known as dish towels), studied as one-layer, and two-layer expected to be better; and good-quality cotton T shirts in 2 layers (with a stitched edge to prevent stretching). In flat-cloth experiments, tea towel, cotton 600 TPI in two layers, and cotton 600 TPI with flannel 90 TPI, performed well, but two-layer cotton 80 TPI did not. Multiple layers should be used, at least two, and preferably three or four; however there is a trade-off in that this increases the resistance to breathing. This is not a systematic review; however, we included all the articles that we identified in an unbiased way. We did not include grey literature or preprints.