A Duke University study comparing medical vs home-made masks has found that the droplet count (ie. how much it leaks) varies significantly and we should pay attention to what will provide adequate protection against Covid-19.

Below shows the 14 masks studied and the results of the droplet count assessment – the findings are:

  • Masks 1 & 14 are surgical and fitted N95 masks, which are most effective. Mask 2 is a valved N95 which is also adequate (valves are somewhat topical at the moment)
  • Surprisingly the polypropylene (2 layer and combined with cotton) masks, number 4 & 5, also provide good protection with low droplet count. “Swath” which is polypropylene mask material also works well
  • Masks 7, 8 & 13, representing pleated 2 layer cotton, also provide good protection
  • But as we get to the other cotton masks, 3, 6, 9 & 10, which are 1 layer cotton, the protection drops off and
  • Loose fitting neck fleece (11) and bandana (12) do not provide sufficient protection. Fleece shows even more droplet count than control (no mask) and there is a hypothesis that it breaks large droplets into smaller droplets, allowing greater infection spread

So the takeaway is – medical masks are best, but can be expensive and limiting due to single use – 2 or even 3 ply cotton masks, fitted well, are a good substitute for the duration of the pandemic, washed frequently.


  • https://advances.sciencemag.org/content/early/2020/08/07/sciadv.abd3083