The best fabric for making a homemade COVID mask is a breathable material which low- and high-speed droplets can’t get through.
Experts at the Mechanical Science and Engineering University of Illinois have tested different common household fabrics.
They identified simple T-shirts as a potential material for homemade masks since they are made of breathable fabrics and are able to block droplets.
They also found that a two-layer mask made from new fabric that was a cotton-polyester mix works as well as a medical mask.
Coronavirus is thought to be spread by the transmission of respiratory droplets produced when an infected person talks and coughs, sneezes or even breathes.
The Centers for Disease Control and Prevention recommends wearing homemade cloth face coverings in public places.
However, the type of fabric and number of layers appear to be important in protecting against infection.
The droplets released come in different sizes and different speeds, therefore the fabric has to be resistant.
On the other hand, highly impermeable materials are generally less fit to breathe through.
A mask with poor breathability forces the air to move through the sides while giving a false sense of safety.
Professor Taher Saif and his team tested 10 common household fabrics to find out what fabric has both the droplet blocking ability and breathability required.
The masks were made from a variety of materials, such as polyester, cotton, silk and mixed fabrics.
They compared properties of these fabrics with the quality masks that reach medical or dental standards.
They found that for typical household fabrics, for example, a single layer of a T-shirt can block 40 percent of droplets.
When they used a new T-shirt made with 60 percent cotton and 40 percent polyester fabric in two layers, surprisingly, the droplet blocking was increased to 98 percent.
Breathing through the mask was easy while the efficiency was higher than the medical mask.
They suggest a two-layer cotton mask fabric can maximise both breathability and droplet resistance.
The study’s authors wrote:
“We found that most home fabrics substantially block droplets, even as a single layer.
With two layers, blocking performance can reach that of surgical mask without significantly compromising breathability.”
One difference between medical masks and household fabrics is that the first is made of hydrophobic material and the latter is hydrophilic.
Hydrophobic materials are water repellent whereas hydrophilic fabrics soak up water.
The study’s authors explain:
“Furthermore, we observed that home fabrics are hydrophilic to varying degrees, and hence soak water.
In contrast, medical masks are hydrophobic, and tend to repel water.
Incoming droplets are thus soaked and ‘held back’ by home fabrics, which might offer an as of yet untapped and understudied advantage of home-made cloth masks.
Overall, our study suggests that most double-layered cloth face coverings may help reduce droplet transmission of respiratory infections.”
The study was published in MedRxiv (Aydin et al., 2020).