Fabric Masks: How to sew a good one

After a year of sewing masks and struggling to decide which fabrics are likely to provide enough filtration... I have data. After reading dozens of papers... I know what to make of it. This is my place to share it with you.

Key ideas:

  • Woven cotton is ok but not great. Cotton masks help reduce transmission and so are effective for public health. But if you want to protect yourself with a high level of filtration... incorporate a better fabric.
  • Non-woven polypropylene and non-woven polyester and flannel are better than cotton. For the same level of breathability, they provide better filtration. Two layers of a medium-weight interfacing will hugely improve your mask's filtration, with little impact on breathability, but the stiffer construction may require adjusting your sewing pattern.
  • Washing is fine. Ten machine wash/dry cycles with a laundry bag don't affect filtration.
  • Particle size is a complex topic without which we can't properly interpret fabric filtration data nor public health recommendations.

To dig deeper, follow these links:

Data summary for sewists

An explanation of what fabrics I had tested and the results, stated as plainly and simply as I can manage, with links to specific fabrics.

Data details for scientists

Details of my experiment and mathematical analysis.

My mask pattern

My mask pattern, compatible with the stiffness of 2 or 3 layers of 65gsm non-woven (such as OlyFun or SmartFab Double-Thick).

On particle sizes

Particles >10μm are filtered well by most fabrics, resulting in clear reduction of community transmission with mask use regardless of type of mask. However, 1μm to 10μm particles also can be infectious, and so excellent protection for the mask wearer necessitates adequate filtration in this range as well. Particle sizes used for filtration testing vary across standards and studies.

Layering Single layer data is not enough, since the first layer in a stack-up seems to filter with higher efficacy than subsequent layers.

Last updated 25 April 2021
© Anna Mitros
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