This page has a summary of the information that we think is most important.

We are a team of academics, physicians, trainees, people who sew, and other volunteers.  We've been working on identifying published, peer-reviewed literature to inform the choice of materials and designs for cloth masks, communicating around materials and design, and curating high-quality information on mask use and mask cleaning.

At present, this site and all our work is on a voluntary basis, without funding.

Our academic work includes an opinion piece available here and a narrative review available here. Our plain language summary of that review is available here, and a longer article here. This website incorporates newer relevant peer-reviewed work as soon as we identify it.


  • Plain woven cotton, at least 100 threads per inch

  • Flannel, either cotton or poly-cotton blend, at least 90 threads per inch

  • Tea towel material

  • Heavy, good quality, cotton T shirt material

  • At least one layer of non-woven industry-grade spunbond polypropylene, recommended by Health Canada and the WHO.  

​With fabric that stretches, such as any knit, for example, T shirt fabric, use a design with edge stitching to prevent the cloth being stretched when worn, which will increase the size of gaps in the material and affect filtration.  


  • 3 or 4 layers 

  • Combine cotton/flannel against the face with polypropylene for middle or middle and outer layers.

  • If you have a pocket mask that doesn't contain sewn-in polypropylene, don’t use a disposable filter, instead use a rectangle of washable polypropylene.


There is a trade-off with increased layers: they provide increased filtration efficiency, but also increase the resistance to breathing, which may lead to discomfort. Increased resistance with increased layers also leads to increased leak around the edges, decreasing the efficiency of the mask.

Double masking

  • Double masking is essentially a method of layering, which our evidence review and subsequent new studies have identified as useful ways to increase filtration.

  • Watch out for breathability, be sure you are comfortable in the double mask, and that the extra thickness is not making the leak around the edge actually worse. The aim is for most of each breath, in or out, to go through the material.

  • Make sure at least one mask has at least one layer of non-woven industry-grade spunbond polypropylene as recommended by Health Canada.

  • Wash both masks after each use. Industry grade spunbond polypropylene can be hot washed but hang to dry - it will melt in a tumble dryer or if ironed.

  • If neither mask is a pocket mask, and neither has polypropylene (or you are not sure if it has polypropylene), you can put a rectangle of washable polypropylene between the two masks, and the outer mask will hold it in place.


Cloth masks should not be placed on:

  • children under 2

  • anyone unable to remove them without assistance

  • anyone who has trouble breathing

Remember not to use detachable parts such as toggles for young children because they are a choking hazard.​

Our academic evidence summary is available here, a plain language version is here, and our guidance on selection of design and cloth for masks is here.

Canadian public health advice is available here; CDC advice here, WHO advice here.

Kindness & Altruism

Though we are sure that many kinds of cloth block particle transmission, including aerosols, and including viruses, we don’t have direct evidence from clinical trials that wearing a mask reduces actual disease transmission in a community setting.  We suggest wearing a mask altruistically, with confidence that this is reducing the contamination of the environment. We suggest remembering people who rely on lip reading to understand what is said.  We suggest withholding judgement on those not wearing masks, given that their personal circumstances and physical health are unknown.