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As the number of people making their own reusable fabric face masks continues to grow, a University of Otago fibre and textile sciences specialist has produced guidance on the best materials to use.
Mask use is mandatory on domestic flights from Auckland, and will become mandatory for anyone travelling on public transport throughout the country from 11.59pm on August 30, under new government rules for Alert Level 2.
Prof Raechel Laing said the Ministry of Health suggested a few masks were needed for each member of a household and some form of face covering was "better than nothing" when in public.
Based on present knowledge and guidelines from the World Health Organisation, she has made a list of material types that would be best for making reusable cloth face masks.
"Three layers of fabric are typically required for this type of mask, depending on both the fabric used and whether or not the mask design provides for an insert filter."
Prof Laing said the inner layer was in contact with the face, so soft and absorbent material would be best.
"That is, a hydrophilic, closely woven structure from cotton/cotton blends or silk."
She suggested the middle layer should be either a filter or a non-woven structure made from a melt-blown or needle-punched material.
The third layer was exposed to the environment, so it needed to limit external contamination.
That could be done by using a layer of hydrophobic material (a closely woven structure) such as polyester, polyamide/blends, and cotton.
"While coating fabric for an outer layer, or using a ‘sprayproof’ coated fabric, enhances barrier resistance, this tends to block interstitial spaces in the fabric and ... adversely affects ease of breathing.
"Unfiltered air from the wearer may be released via the sides of the mask during exhalation. Coating is therefore, not recommended."
Prof Laing said the masks needed to be washed in hot water with soap or laundry detergent, so the selection of fabrics and materials needed to be considered.
Hot water might affect the shape and stability of the mask.
"Use of elastic materials or very porous knit structures, is not advised because these stretch during use, increasing interstitial spaces and thus reducing filtration efficacy.
"A further reason is that many elastic materials are adversely affected by washing at the high temperature required for cleaning."