< Masks

What are the different types of masks?

Text updated on 2020-05-27


No mask offers complete protection against the emission and reception of viral particles. The type of mask to be used depends on its availability and cost, and the risk of contamination to which one is exposed. Properly handled, it will always act as a barrier.

There are four different categories of masks, materials, and designs:

* Surgical masks: these are the disposable masks normally used by health care workers. They have 3 layers of non-woven fabric: a hydrophobic outer layer that prevents droplets from entering the mask; an intermediate layer that blocks bacteria, body fluids and particulate contaminants; and the inner layer in contact with the nose and mouth that absorbs moisture.

- Protective respirators: They are called FFR--filtering facepiece respirators--and are of several types. Their primary purpose is to protect caregivers who are in prolonged contact with highly contagious patients.
In Europe, Russia, and Maghreb countries, they are approved as FFPs (followed by a number that indicates the filtration efficiency). They are also known as P1 to P3, abbreviated to FFP1-FFP3. In the United States, Mexico, Turkey and India, they are certified as N, R, or P according to their oil resistance (followed by the percentage of filtration): N95, N99, or N100. In China, they are certified as KN or KP95, in Australia and New Zealand, P2, in South Korea, Korea 1st class/KF94, in Japan, DS/DL2, in Brazil, PFF2.

- Elastomeric respirators (Elastomeric respirator): with filter cartridges (cartridge) or filters, they are comparable to protective respirators, but reusable. They are normally used to protect against gases or powders; they are not common among caregivers.

- Fabric masks: Washable and reusable masks that can be made at home. They have less filtration power than other types of masks, but they can block the droplets emitted when coughing, sneezing, talking, and breathing. Conversely, they can absorb droplets emitted by a person talking to them.

The important elements that determine a mask's ability to prevent the spread of the virus are its filtration capacity and adhesion to the face: particles should not be able to enter or exit through or around the mask.

Filtration power (percentage of particles that are blocked by the mask): changes with the size of the particles, their speed, and electrical charge.

- surgical masks:

in entry: from 22% to 94% for surgical masks, from 19% to 44% for dentist masks

in output: from 22% to 95% for surgical masks, from 18% to 38% for dentist masks

This enormous variation is due to the materials used, the purpose of the mask (surgeons, dentists, nurses...) and the fact that there is no single certification standard as for respirators.

- protective respirators :

input: 95%, 99% and 99.97% for type N (the number indicates the percentage of filtration); 80%, 94% and 99% respectively for FFP1, FFP2 and FFP3.

at the outlet: of the same order of magnitude for ventilators without valve, close to 0% for ventilators with valve (because they let the outgoing air flow through).

- fabric masks: the filtration power, in entry and exit, generally ranges from 70% to 97%. The most efficient (94-97%) masks combine a fabric that filters electrostatically (e.g., cloth, silk, flannel) and another that filters mechanically (e.g., fine weft cotton). Synthetic silk alone (0-28% filtration) or satin alone (3-25%) should be avoided.

Adhesion to the face

- surgical masks: they let air pass underneath and through the sides.

- Protective respirators: if they are well adjusted to the face, the adhesion is almost total. Health care personnel who use them are trained to do so in the best possible way and an adhesion test is often necessary.

- fabric masks: these are normally less or as adherent as surgical masks, depending on how they are made.

Tip: Adding a piece of nylon sticker on top of the mask improves adhesion and increases filtration efficiency by 15% to 50%. This has been demonstrated over a period of 2 hours. It is currently difficult to know if this method works (moisture retention?) for longer periods of time.

A computer graphic in English on the different types of masks.

https://www.cdc.gov/niosh/npptl/RespiratorInfographics.html


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Sources

Continuous use of masks reduces the transmission of the influenza virus from sick children to the adults who care for them.

MacIntyre, C. R., Cauchemez, S., Dwyer, D. E., Seale, H., Cheung, P., Browne, G., Fasher, M., Wood, J., Gao, Z., Booy, R., & Ferguson, N. (2009). Face mask use and control of respiratory virus transmission in households. Emerging infectious diseases, 15(2), 233-241.

FFR masks, denomination.

CDC - NPPTL - NIOSH-Approved Particulate Filtering Facepiece Respirators. (2020, April 9). Retrieved April 29, 2020.

Elastomeric respirators.

National Academy of Sciences, Engineering and Medicine. (2018, December 6). Elastomeric Respirators. Retrieved April 29, 2020.

Filtration efficiency of several types of respirators according to different tests.

Rengasamy, S., Eimer, B. C., & Shaffer, R. E. (2009). Comparison of nanoparticle filtration performance of NIOSH-approved and CE-marked particulate filtering facepiece respirators. Annals of Occupational Hygiene, 53(2), 117-128.

Institute of Medicine. (2016). Reusability of Facemasks During an Influenza Pandemic: Facing the Flu. Chapter: 2 Characteristics of Respirators and Medical Masks. Washington DC: The National Academies Press.

Filtration efficiency of several types of masks. Tested with NaCl (particle size approx. 100 nm) and Paraffin Oil Test.

Jung, H., Kim, J., Lee, S., Lee, J., Kim, J., Tsai, P., & Yoon, C. (2014). Comparison of filtration efficiency and pressure drop in anti-yellow sand masks, quarantine masks, medical masks, general masks, and handkerchiefs. Aerosol Air Qual Res, 14(14), 991-1002.

A layer of nylon (pantyhose) around the head above the surgical mask improves adhesion to the face and, by reducing air passage, greatly increases filtration efficiency.

Mueller, A. V., & Fernandez, L. A. (2020). Assessment of Fabric Masks as Alternatives to Standard Surgical Masks in Terms of Particle Filtration Efficiency. medRxiv.

Filtration efficiency of fabrics commonly used for the production of masks.

Konda, A., Prakash, A., Moss, G. A., Schmoldt, M., Grant, G. D., & Guha, S. (2020). Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks. ACS Nano. doi: 10.1021/acsnano.0c03252

According to the standards of the French Association for Standardization (Afnor), the filtration efficiency of the material for particles of 3 μm (3 thousandths of a millimeter) or more must be greater than or equal to 90% for category 1 masks, and greater than or equal to 70% for category 2 masks. These masks therefore filter the large droplets expelled by a patient with COVID-19, droplets with a diameter of about 5 μm.

AFNOR SPECS76-001, 28 April 2020, Barrier masks: Guide to minimum requirements, test methods, manufacture, and use.

The standards are NIOSH-42CFR84 in the USA, EN 149:2001 or EN 149:2009 in Europe, GB2626-2006 in China, AS/NZS 1716:2012 in Australia/New Zealand, KMOEL-2017-64 in South Korea, JMHLW-2000 / Notification 214, 2018 in Japan, ABNT/NBR 13698:2011 in Brazil, NOM-116-2009 in Mexico.

NPPTL Respirator Assessments to Support the COVID-19 Response. The National Personal Protective Technology Laboratory (NPPTL). Centers for Disease Control and Prevention. Updated: 13 May 2020.

Further reading

Why put on a mask?

How do you put on and take off your mask?

Do I have to wear a mask if I don't have any symptoms?

Can a mask be reused?