According to this study:
And here are some tips for no-sew masks:
They aren’t suitable for use in a hospital and probably not for use if you are home with somebody you know likely has the China virus. but for general going shopping, home-use, it’s an additional tool along with the hand-washing, not touching your face, etc (and they help with not touching your face): https://youtu.be/CbRsb0T7Oz8
Here’s another one, and she shows you how to make them more effective still by including a filter (the filter part is disposable, don’t reuse more than once): https://youtu.be/lOe_8z8k01U (the filters are going to be harder to find now, I don’t know if any home improvement stores are open. Try ebay)