Abstract
To function as source control, a fabric mask must be able to filter micro-droplets (≥5 µm) in expiratory secretions and still allow the wearer to breathe normally. This study investigated the effects of fabric structural properties on the filtration efficiency (FE) and air permeability (AP) of a range of textile fabrics, using a new method to measure the filtration of particles in the described conditions. The FE improved significantly when the number of layers increased. The FE of the woven fabrics was generally higher, but double-layer weft knitted fabrics, especially when combined with a third (filter) layer, provided a comparable FE without compromising on breathability. This also confirmed the potential of nonwoven fabrics as filter layers in masks. None of the physical fabric properties studied affected FE significantly more than the others. The variance in results achieved within the sample groups show that the overall performance properties of each textile fabric are a product of its combined physical or structural properties, and assumptions that fabrics which appear to be similar will exhibit the same performance properties cannot be made. The combination of layers of fabric in the design of a mask further contributes to the product performance.
Highlights
Face mask manufacturers are confronted with a lack of reliable information on the factors that determine the performance of fabric masks
This study investigates the effect of fabric structural properties on the filtration efficiency (FE) and air permeability (AP) of masks, both considered crucial properties affecting the functionality of this type of mask
This intervention was preempted by recommendations made by the World Health Organization (WHO), based on evidence that the COVID-19 virus is primarily transmitted between people through contaminated respiratory droplets (≥5 μm in diameter) and secondary contact routes [4]
Summary
Face mask manufacturers are confronted with a lack of reliable information on the factors that determine the performance of fabric masks (generally referred to as “cloth masks”). Wearing of face masks made of ordinary textile fabrics (in addition to vigilant hand hygiene and social distancing) has been put forth as the most effective means to mitigate disease transmission by preventing outward transmission of contaminated droplets by an infected person [1,2,3]. This intervention was preempted by recommendations made by the World Health Organization (WHO), based on evidence that the COVID-19 virus is primarily transmitted between people through contaminated respiratory droplets (≥5 μm in diameter) and secondary contact routes [4]. The fabric masks are designed to act as “source control”, meant to provide sufficient filtration efficiency to stop the transmission of micro-droplets from an infected person to the environment [5]
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