After weeks of insisting that only medical professionals or people infected with COVID-19 have to wear face masks, The Centers for Disease Control and Prevention (CDC) has updated their guidelines on wearing face masks in public to recommend that everyone, whether sick or not, should wear a face mask made of fabric. This is especially important in public environments (e.g. grocery stores and pharmacies), where other measures such as keeping a distance of 2 meters are impossible. DIY homemade face masks now play an important role in the fight against COVID-19 pandemic, but the type of fabric used is, according to scientists, the key to its effectiveness.
The change in recommendations resulted from new information on the symptoms of coronavirus. A significant number of people with the virus have little to no symptoms, the CDC reports. There is also a long incubation period during which people infected with the virus have no symptoms. In both cases, these people are still contagious to others.
DIY Bandana mask with coffee filter – Instructions from the CDC
On their website, the CDC published a few instructions for DIY homemade face masks with and without sewing. According to instructions, one should use tightly woven cotton fabric, T-shirt fabric will also work well, if necessary. A mask with a filter, on the other hand, can be quickly made from a bandana cloth, a coffee filter and hair bands. So there are several options for household items that everyone already has at home. But which material is the best for a DIY protective mask?
According to scientists, these materials are the most suitable
US scientists have set themselves the task of identifying household materials and items that can be used to better filter microscopic particles. Recent tests have shown good results: air filters, vacuum cleaner bags, pillowcases with a thread density of 600 and flannel fabric with a thread density of 180.
Scott Segal, chair of anesthesiology at Wake Forest Baptist Health in North Carolina, conducted a series of tests to determine how effective they would be as face masks. To determine the protective properties of homemade fabric masks, a team of doctors and scientists tested 13 different designs of approximately 400 masks made by community volunteers. The aim was to find out which type of mask can filter virus particles with a diameter of 0.3 to 1.0 micrometers compared to surgical masks and N95 respirators. The test team found that the effectiveness of the masks was very different. The test team found that the effectiveness of the masks was very different. The best homemade masks achieved a filtration rate of 79% compared to surgical masks (62% to 65%) and N95 masks (97%).
The most powerful designs were a mask made of two layers of high quality, heavy quilt fabric, a two-layer mask made of thick batiste fabric and a two-layer mask with an inner layer of flannel and an outer layer of cotton. Single-layer masks or two-layer designs made from light, low-quality cotton had the worst results.
So if you want to sew a face mask, you should use a high-quality, thick cotton fabric. And if you’re not sure if the fabric you have at home is thick enough, Dr. Segal plans to do the following simple test. Hold the fabric against bright light. If light falls through the fibers very easily and you can almost see the fibers, it is not a good material. If it is a denser fabric made of thicker material and does not let as much light through the fabric, this is the material you want to use.
The biggest challenge when choosing a homemade mask material is to find a fabric that is dense enough to trap virus particles but also breathable enough to actually wear it.
Which is the best filter for DIY homemade face masks?
Yang Wang, assistant professor of environmental engineering at Missouri University of Science and Technology, worked with his PhD students to study different combinations of materials – including air filters and fabrics. Dr. Wang’s group tested two types of air filters. An HVAC filter for allergy sufferers worked best, picking up 89 percent of the particles with one layer and 94 percent with two layers. The other air filter covered 75 percent with two layers, but needed six layers to reach 95 percent. To find an air filter that is similar to the ones tested, look for a MERV (Minimum Efficiency Reporting Value) of 12 or higher.
The problem with air filters is that they can potentially release small fibers that would be risky to inhale. So if you want to use a filter, you have to insert the filter between two layers of cotton fabric.
Dr. Wang’s group also found that when using certain fabrics, two layers offered far less protection than four layers. A pillowcase with a thread density of 600 recorded only 22 percent of the particles in two layers compared to four layers with a filtration rate of almost 60 percent. A thick woolen scarf filtered 21 percent of the particles in two layers and 48.8 percent in four layers. A scarf made from 100 percent cotton had the worst results: only 18.2 percent in two and 19.5 percent in four layers. The group also tested coffee filters that showed a filtration efficiency of 40 to 50 percent when stacked in three layers – but they were less breathable than other options. Scarves and cotton bandanas can therefore protect more effectively if they have a filter such as coffee filter.
Wash the reusable masks after each wear
To ensure that masks are as effective as possible, regular washing at a minimum of 60°C is essential. Since the mask should be washed after each wear, it makes sense to make several masks. Experts advise avoiding bleach and harder chemicals, as these can damage the fabric threads. Wear the masks only briefly and never all day – for example, if you absolutely have to leave the house to buy important things such as food and medication. Experts emphasize that masks can give a false sense of security. It is important to continue to follow all other guidelines for protection against Covid-19. No mask is as effective as social distance and good hygiene. These are still the best ways to protect yourself and others.
You can see the patterns and instructions on the web page of CDC.