Promoting simple do-it-yourself masks: an urgent intervention for COVID-19 mitigation

Matthias Samwald and co-authors
14 min readMar 18, 2020

Dr. Fabian Svara (1), Angus Yiu-Ting Choi BSc, MPhil (2), Dr. Matthias Ober (3), Dr. Joergen Kornfeld (4), Assoc. Prof. Dr. Matthias Samwald (5)*

1) Biomedical research, Bonn, Germany
2) Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong
3) Product Design and Process R&D, Corteva Agriscience; Midland, MI, USA
4) Brain and Cognitive Sciences, McGovern Institute, Massachusetts Institute of Technology; Cambridge, MA, USA
5) Center for Medical Statistics, Informatics and Intelligent Systems; Medical University of Vienna, Austria

* corresponding author (matthias.samwald -at-


We demonstrate that widespread use of masks by the general population could be an effective strategy for slowing down the spread of COVID-19. Since surgical masks might not become available in sufficient numbers quickly enough for general use and sufficient compliance with wearing surgical masks might not be possible everywhere, we argue that simple do-it-yourself designs or commercially available cloth masks could reduce the spread of infection at minimal costs to society.


Because an estimated 15% of COVID-19 patients require hospitalization and 5% require intensive care (Z. Wu and McGoogan 2020), the ongoing COVID-19 pandemic has the potential of posing a substantial challenge to medical systems around the world (Remuzzi and Remuzzi 2020; Grasselli, Pesenti, and Cecconi 2020). The number of simultaneously ill patients must therefore be kept low by reducing the basic reproductive number of the infection. In many realistic scenarios, this can only be achieved by applying mitigation techniques vigorously and continuously, up until the point where a vaccine or an effective therapy becomes available (Neher et al. 2020; Anderson et al. 2020). However, that point may well not be reached until many months after initiation of public health responses (Adalja, Toner, and Inglesby 2020; Lowe 2020).

Respiratory droplets constitute an important transmission pathway of COVID-19 (Y.-C. Wu, Chen, and Chan 2020). Therefore, an intervention that can reduce the amount and spread of respiratory droplets shed by infected persons will help reduce new infections, either directly or by decreasing the amount of virus deposited on fomites, on which coronaviruses likely remain contagious for several days (Kampf et al. 2020; van Doremalen et al. 2020). For this reason, the World Health Organization (WHO), Center for Disease Control (CDC) and Robert Koch Institute (RKI) recommend the use of face masks by infected persons. However, they do not recommend the routine use of face masks by ‘healthy’ persons (CDC 2020; WHO 2020; RKI 2020). This is in spite of the fact that COVID-19 is often characterized by a period of mild, common cold-like symptoms, during which patients can already spread the infection (Woelfel et al. 2020). Furthermore, some studies indicate that transmission may occur by presymptomatic cases (Du et al. 2020; Nishiura, Linton, and Akhmetzhanov 2020). Since mild, cold-like symptoms might not be sufficiently concerning to cause an effective change in behavior, behavior that minimizes the spread of respiratory droplets in general must become the norm.

Face masks as an effective public health intervention

Wearing surgical masks is a key part of interventions in China and other East Asian countries. China is taking strong measures to ensure wearing of face masks in public spaces and workplaces and has issued public guidelines that recommend different types of masks based on exposure risk (NHC 2020). South Korea, Singapore and Japan recommend covering the mouth and nose based on different criteria (when unwell in Singapore, in crowded places in South Korea , when coughing or sneezing in Japan) (Singapore Ministry of Health 2020; Korean Ministry of Health and Welfare 2020; Japanese Ministry of Health, Labour and Welfare 2020). In these countries, surgical face masks are being provided to households by the governments ( 2020; Channel News Asia 2020; Yonhap News Agency 2020). Importantly, the use of face masks is a culturally accepted practice, often performed to protect other people when a person suffers from mild respiratory symptoms in Japan and other east asian countries (Horii 2014).

Suggestively, among countries with significant outbreaks (>100 cases as of March 10, 2020, 7 days ago), countries having a cultural norm of wearing masks or where the government recommends mask use by the general public have drastically lower growth rates of confirmed cases after initial outbreak containment in comparison to other countries (Figure 1).

Figure 1: Different countries are experiencing different exponential growth patterns.
a) Confirmed cases by country. b) Daily growth rate, averaged over 7 days starting from March 10, 2020. c) Histogram of data in panel b. Data source: Johns Hopkins University Center for Systems Science and Engineering (CSSE 2020).

While surgical masks might not provide protection from respiratory infection at the level of sophisticated masks (e.g., FFP3/N95 masks), they decrease the transmission of droplets or aerosols containing viral particles by mask wearers (Johnson et al. 2009). They could therefore play a role next to social distancing and hygiene measures in slowing the spread of the disease. Furthermore, there is evidence that even simple surgical masks do provide some degree of protection to the wearers themselves (Radonovich et al. 2019; Loeb et al. 2009; Makison Booth et al. 2013; Li et al. 2008; Lai, Poon, and Cheung 2012), particularly in combination with handwashing and other social distancing measures (Jefferson et al. 2008; Suess et al. 2012). During the previous SARS outbreak, daily wearing of surgical masks in the community significantly reduced the chance of infection in both low and high population density areas (Lau et al. 2004; J. Wu et al. 2004).

However, most countries outside East Asia have made the striking decision to exclude wearing of face masks from their interventions. Face masks are in short supply in many countries, and some officials claimed that wearing face masks is ineffective for the general public (e.g., (Leah Asmelash 2020)). Furthermore, people in most regions outside East Asia are still averse to wearing such masks, i.e., there is no established culture of wearing face masks in public.

This leads to disconcerting scenarios: while several countries are heading towards lockdown, citizens crowd in public transport, pharmacies and supermarkets without wearing face masks of any kind.

Simple, culturally acceptable face masks as an immediate intervention

The urgent problem of insufficient mask availability and cultural acceptance could be mitigated by devising a simple do-it-yourself (DIY) method for creating face masks that can be worn in public, and motivating widespread adoption. It was shown that even simple DIY masks (e.g., made of T-shirt cloth) can modestly, but significantly reduce the amount of infectious particles expelled by persons wearing them (Davies et al. 2013; van der Sande, Teunis, and Sabel 2008). More recently, during the COVID-19 outbreak, researchers from the University of Hong Kong-Shenzhen Hospital devised a DIY face mask design and claimed to achieve effective filtering (Hong Kong Consumer Council 2020; South China Morning Post 2020). Historically, relatively simple mask designs were used even by medical professionals, with some evidence backing their effectiveness (see Appendix).

The potential concern that wearing masks may convey a false sense of security to the wearer seems to be empirically unfounded. Instead, wearing masks is associated with better personal hygiene practice, including increasing frequency of hand washing and reducing social contact (Wada, Oka-Ezoe, and Smith 2012). The reinforcements of these personal hygiene habits would also help in reducing the spread of infection.

Therefore a public health intervention for promoting DIY mask use could have significant positive impact, even if it just serves as an interim step until medical-grade masks are available and sufficiently accepted. Such an intervention should strive towards the following goals:

  1. Ease of creating the DIY respiratory protection
  2. Sufficient effectiveness to warrant use
  3. Ease of adoption, i.e., comfortable to wear, culturally acceptable
  4. Wide-spread knowledge and promotion, ideally through public institutions
  5. Include messaging encouraging positive behaviour, e.g., encouraging regular cleaning of face masks, avoiding the creation of an unwarranted sense of security through mask wearing which might decrease social distancing, discouraging face touching, and avoiding blockage of adoption of other, more effective means of protection

DIY masks would not need to imitate the shape of surgical masks. Potentially, simply wrapping a suitable, large cloth around the face is easy to implement (Fig. 2), would arguably be more socially acceptable than surgical masks, and would be superior to a complete lack of face mask use.

Figure 2: Simple face cloths for decreasing the spread of infectious droplets (Source: Pexels 2020; Unsplash 2020).

We would like to highlight that many of the currently taken mitigation strategies will have severe negative economical and societal consequences which are nevertheless perceived as being without alternative. These measures will be effective in reducing COVID-19 transmission, but could potentially be shortened through an earlier “flattening of the curve” which could be achieved by early, broad adoption of face mask use.

We therefore urge policy makers to consider the usage of face masks — in all forms — in public spaces, and to follow the governments of those countries (e.g., South Korea, Japan) that included wearing masks in their effective COVID-19 mitigation measures.


We want to thank all members of the research community who gave valuable feedback while creating this manuscript.

Conflicts of interest

The authors declare no conflicts of interest.


Historical use of face masks

There is a long history of using fabric and easily accessible materials in mask production. In the early 20th century, healthcare providers used facemasks that were made of double gauze layers, which were reported to reduce the incidences of meningitis and upper respiratory infection symptoms (Weaver 1918). They have also been used in military barracks as primary prevention of communicable diseases (Capps 1918). Various different materials, such as celluloid and cheese-cloth, were used in masks for subsequent pandemics and infection outbreaks (McNett 1949; Viseltear 1974). The paper mask, the origin of the modern surgical mask design, was constructed using two sheets of water repellent paper with a cellulose padding inside to serve as a filter layer and showed efficacy in filtering Staphylococcus aureus (Shooter, Smith, and Hunter 1959). Together, these interventions showed that simple fabric materials may provide some degree of protection from infection.

Mechanism of protection from the wearer and by the wearer

Face masks serve in two ways to limit disease transmission. First, they protect the wearer by inhaling infective particles and aerosols. To be fully effective, fine mesh size masks are needed that are capable of filtering fine particles; ideally down to the size of the particle size of the actual virus. Such masks are particularly helpful for persons exposed to high concentrations of infective aerosols, such as health care workers. Second, they prevent emission of infective droplets into the environment. For this purpose, even masks with a larger mesh size may be helpful. According to Scharfman et al., 20016 and Bourouiba et al., 2014 (Scharfman et al. 2016; Bourouiba, Dehandschoewercker, and Bush 2014), even relatively large respiratory droplets can travel forward and upward by several meters. Droplets may rise high enough to get carried into ventilation systems. An important factor for this behaviour is droplet evaporation while airborne. This effect causes droplets that would be large enough to be captured by cotton cloth (>20 µm) to shrink or aerosolize while airborne and stay suspended for extended periods.

Once emitted into the environment, the droplets may eventually deposit on surfaces which may become contaminated. As the surface viability of coronaviruses can approach several days (van Doremalen et al. 2020; Kampf et al. 2020), surface accumulation may have to be considered.

A significant quantity of the expelled material is initially not separated into individual droplets; the separation appears to occur in some spatial distance from the mouth (Figure 3). A cloth mask should therefore be able to catch a significant amount of the volume of the expelled material before becoming airborne.

Figure 3: Stages of sneeze ejecta after 8, 21 and 117 ms. Reproduced from (Scharfman et al. 2016).
Note: Presumed to be covered under the fair use doctrine, if you believe the material has been used in an unauthorized manner, please contact the authors to request removal.

In combination, it appears that:

(1) ‘Filtering the cough at the source’ (face mask worn by symptomatic or non-symptomatic patients) prevents distant contamination sideways, downards (due to fallout) and upwards (due to cloud buoyancy) — meters away from the source. Droplets may evaporate where they remain airborne for a prolonged period of time. It is currently not clear to what extent material in evaporated droplets is still infective.

(2) At the source, the emitted liquid should be easier to remove, due to (a) its viscoelastic property; in proximity to the mouth a significant fraction of the liquid is in form of ligaments and not droplets and (b) as they did not have time to evaporate to a small size. Hence a simple cotton cloth or a surgical mask should be able to remove the majority of the liquid component of the emitted material.


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