As New Zealanders are urged to prepare for an imminent second wave of Covid-19, the country's top health official is demonstrating how to correctly use a face mask on social media this morning.
Kiwis have now joined much of the world in masking up to combat Covid-19 - but how do we know if that piece of cloth we've repurposed is doing the job we want it to?
The University of Otago's leading expert on fibre and textile sciences, Professor Raechel Laing, saidthat, with few controlled studies, there were still many knowledge gaps around reusable fabric masks.
And there were a range of factors that determined their effectiveness, from how a mask was positioned on our face, how it fared after repeated washes, how long we wore it for, and the structure of the fabric itself.
Laing saw the big issue as striking a balance between the mask's resistance to spreading or stopping particles, and its suitability for breathing.
"These two fabric performance properties tend to be inversely related, with a material which is an efficient particulate filter typically impairing ease of breathing."
People choosing fabrics for masks at least needed to ensure they could be washed in hot water with soap or laundry detergent.
She also discouraged the use of elastic materials or containing elastane filaments, such as Lycra, as the main fabric along with those with porous knit structures, as they typically stretched during use and made for less effective filters.
"A further reason is that many elastic-type materials are adversely affected by washing at the high temperature required for cleaning."
Rather, three layers of fabric were typically needed for reusable cloth masks, and each of these played a different part.
As the inner layer was in contact with the face, it needed to be soft and absorbent, while the middle layer, often non-woven, served as a filter.
The outer layer, exposed to the environment, limited any outside particles entering and could be a closely-woven structure made from polyester, cotton or polyamide blends.
While some people might opt to use coating fabrics as outer layers for extra protection, Laing said this could reduce a mask's permeability to air or vapour, thus making it harder to breathe.
"Further, unfiltered breath from the wearer may be released via the sides of the mask during exhalation. Coating is therefore not recommended."
While material cut from old t-shirts has been widely recommended for masks, Laing said there were some downsides.
"Being knit structures, they are more porous than woven fabrics, and are also extensible," she said.
"This means the interstitial spaces between or among the yarns increase, potentially resulting in a fabric less resistant to particle transmission."
However, knit fabrics also varied in thickness, with thicker fabrics more resistant to particle transmission than thin ones.
"The disadvantage of a thicker fabric is that it is warmer over the covered area of the face."
On the plus-side, masks made from old T-shirts were typically softer than woven structures, making them more comfortable to wear.
What about tea towels?
"These come with different structures and fibre content - ranging from woven, loop pile, needle-punched, to cotton, linen and polyester - and would be a reasonable source if it was a woven structure with closely packed yarns," she said.
"And as conventional tea towels can be washed at a high temperature, this is an advantage."
Lesley Gray, a senior lecturer at Otago University's Department of Primary Health Care and General Practice, said as New Zealand had adopted mask use so quickly it was understandable Kiwis might be nervous about wearing them in public.
"As we become more comfortable and socialised to wearing masks we can show our individuality by the designs we choose," she said.
"Now is the time for Aotearoa to make mask wearing on public transport a routine thing at level 2 and above.
"We need to get over our embarrassment and start appreciating everyone's unique mask identity - and not forgetting good hand hygiene and physical distancing where possible."
