Now that the health authorities recommend wearing hygienic masks to avoid contaminating the coronavirus (especially asymptomatic people) and given the shortage of this product, as a last measure if we do not have hygienic masks, we can make ours at home. Of course, they will be less effective.
At the moment, the recommendations that are being made are in line with reserving the self-filtering masks, that is, those that carry the acronym FFP, to the health workers . This type of mask protects the person who wears it from getting coronavirus but not others from being infected, as it does not filter the exhaled air. The hygienic or barrier ones do protect from infecting others but they do not prevent contagion from the person wearing it.
If at this point we have decided to make our own hygienic masks at home, we must know that there are more or less effective materials for their preparation. The most filtering in order from highest to lowest are the following: vacuum cleaner bag (86% effective), kitchen towel (73%), cotton-polyester blend (70%), antimicrobial pillowcase (68%), linen (62%), pillowcase (57%), silk (54%), 100% cotton t-shirt (51%) and scarf (49%) . Of course, it must be taken into account that some fabrics will weigh more than others and that they will be able to adjust more or less to the face.
These data come from a study published on May 22, 2013 in the journal Disaster Med Public Health Preparedness of the University of Cambridge, the objective of which was to verify whether homemade masks could be an alternative to commercial ones when protecting against a flu pandemic. The research evaluated the ability of a series of household materials to block bacterial and viral aerosols. What was seen was that the surgical mask was always the best option , although the homemade ones could also reduce the number of microorganisms expelled. The latter did not ensure the same fit as the surgical ones.
The researchers ultimately concluded that a homemade mask should only be the last resort to prevent droplet transmission from infected individuals, but that it would be better than nothing.
And if two different fabrics are combined, does the efficiency increase?
SARS-CoV-2 is spread mainly through respiratory droplets that an infected person expels by coughing, sneezing, talking, or breathing. These drops can be of different sizes, the smallest are known as aerosols and can easily slip between the openings of certain fabric fibers. What if we combine different tissues in a mask?
A group of researchers at the University of Chicago has just discovered that a homemade mask made with a layer of cotton and two layers of polyester-spandex gauze, a transparent fabric widely used in nightwear, can filter most particles from a aerosol (80-99%) , with a performance close to that of an N95 mask material. If instead of using polyester-spandex gauze together with cotton, natural silk or flannel is used or just a cotton quilt with cotton and polyester wadding, the filtering obtained is similar. Scientists point out that tightly woven fabrics, such as cotton, would act as mechanical barriers against particles, while fabrics that have a static charge, such as certain types of chiffon and natural silk, would act as an electrostatic barrier . Of course, the mask fit is very important because if it is not correct, the filtering efficiency of all the masks can be reduced by half or even more.
The United States CDC (Centers for Disease Control and Prevention) recommends the use of cloth masks to reduce the spread of the coronavirus, even if they are made at home. Surgical and self-filtering are reserved for health workers.
This is how they recommend making a very simple homemade mask.
Referencias: https://www.cambridge.org/core/terms Copyright & 2013 Society for Disaster Medicine and Public Health, Inc. DOI: 10.1017/dmp.2013.43 . https://doi.org/10.1017/dmp.2013.43
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Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks. Abhiteja Konda, Abhinav Prakash, Gregory A. Moss, Michael Schmoldt, Gregory D. Grant, and Supratik Guha. ACS Nano Article ASAP. DOI: 10.1021/acsnano.0c03252
Recommendation Regarding the Use of Cloth Face Coverings, Especially in Areas of Significant Community-Based Transmission https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/cloth-face-cover.html
