Not all face coverings are created equally…
Since the start of lockdown we have been working on the design of our face coverings, it became clear very early in the pandemic that face coverings could theoretically reduce the transmission of covid-19 from asymtomatic individuals harbouring the virus. We wanted to create a face covering that not only looked good but was comfortable, breathable and offered protection from droplet spread.
Peter Hogarth, logistics volunteer wearing his YS face covering
We looked at what was being used as a filter in other face coverings. One of the filters that raised the most concerns was HEPA filters which are made from glass fibres, microfibre, fiberglass and spun glass, so although they can trap 99.97% of airborne particles it is not something that you would want to be breathing through! Interfacing had also commonly been used as a filter, some of which is fusable (i.e. containing glue), the safety profiles of these is not known and they are not hydrophobic fabrics so offer little, if any, protection from aerosolised droplets.
A fabric that showed promise was the material used in bridal gown bags, as it is both breathable and water repellent. We conducted some rudimentary kitchen top experiments which showed this fabric performed well on its own but when combined with a cotton layer this increased transference of moisture through the face coverings.
With thanks for Treasured Brides for the bridal bags and our volunteer seamstresses, Karen Thompson and Rachel Simpson for making up the initial prototypes!
Kitchen top experiments using Peltek
We were discussing this dilemma with Ian Willis, head of procurement, who suggested trialling some of the fabrics they had been experimenting for use in surgical gowns. Peltek, a non-woven polypropylene fabric which is breathable, water-repellent and washable performed well in out kitchen top experiments, 100ml of water sat on these fabrics without any penetration after 24 hours.
Elaine Howard, one of our volunteer seamstresses, brought our attention to an BBC Inside Science programme on face coverings discussing current research. What this highlighted was that very little is know about the effectiveness of different fabrics used to make face coverings and also the huge environmental impact of public use of disposable surgical masks
‘If all citizens of the UK were to use one disposable face mask every day for a year that would create 128 THOUSAND tonnes of unrecyclable plastic waste’ - Prof Miodownik, UCL
Imperial College London
Prof Christopher Pain, from the Department of Earth Science & Engineering at Imperial College London and the lead for ‘Environmental and Aerosol Transmission’ within the ‘Rapid Assistance in Modelling the Pandemic (RAMP), an initiative to inform the work of the Government’s scientific advisors from a diverse range of disciplines is working with Dr Jiansheng Xiang to investigate the effectiveness of masks to reduce exposure to contaminated respiratory droplets/aerosols and particles.
Imperial College partnered with Prof Kumar and Dr Omidvarborna at the Global Centre for Clean Air Research to evaluate the effectiveness of face coverings are varying inhalation/exhalation rates.
They tested the face coverings for removing particles in various size ranges from 5 nanometers up to one micron (click here). In summary, one layer of thick (50gsm) and one layer of thin (30gsm) offers the best protection from nanoparticles.
‘It shows when you increase the number of layers, the face covering will protect individuals (by upto 55+/-16%) within the tested particle sizes. But, as time goes on, the inhalation rate would be different compared to filters with fewer layers (see before and after face masks for 1-h testing)’ - Dr Hamid Omidvarborna, Research Fellow at GCARE
The story continues, GCARE are testing different types and combinations of filter fabrics. We are also doing testing on the fit of face coverings. We hope to develop a rating scale for face coverings and to assess how the filter fabric properties are changed through washing.
