Masks can be made out of cotton or linen fabric. Cloth masks can and should be washed on a daily basis. Thick, densely woven cotton fabrics are best, like quilting cotton or cotton sheets. Stretchy knits aren’t ideal. Hold the fabric up to the light, and the less tiny holes you can see, the better it will be to filter your droplets.
In totality, having a good mask features the striking of a balance. One would want fabric that doesn’t enable droplets to pass through, while making sure you can breathe properly with your mask in place. Looking a mask you can comfortably keep on should be the end goal, even if it doesn’t offer the same level of protection as someone who may be able to endure more layers and a tighter seal.