SINGAPORE - People here donned cloth masks of varied designs when surgical and N95 masks were in short supply earlier this year.

The Government is also distributing free reusable masks, which are available for collection till tomorrow at community clubs and residents' committee centres across the island.

Made of cotton, these free masks provide between 50 and 60 per cent of filtration efficacy.

Now, some people are making their own as well. But what would make for a good reusable mask?

Dr Teo Tee Hui, a council member of The Institution of Engineers Singapore and senior lecturer at the Singapore University of Technology and Design, recommends fabric with good moisture absorption, such as cotton T-shirts or handkerchiefs, as the inner layer, as this ensures the wearer is comfortable.

Those thinking of making their own mask should consider the function, design, ergonomics (efficient and comfortable), aesthetics and manufacturing process.

Citing a study done by Cambridge University, which tested the efficacy of homemade masks in an influenza pandemic, Dr Teo noted that DIY masks with a single layer of cotton can still achieve 50 to 60 per cent of filtration efficacy for particles between 0.02 and 1 micron in size.

According to reports, the coronavirus is approximately 0.12 micron in size. Dr Teo said wearing a self-made mask is better than not wearing one at all.

To improve protection, he recommends double-layer masks, preferably made with a waterproof fabric. Otherwise, the outer-layer fabric can come from pillowcases, including those made of bamboo charcoal, or bed sheets.

He added that the filtration efficacy of the mask does not increase significantly with more layers. Using too many layers could pose a risk to wearers, who may find it difficult to breathe.

He also suggested materials used in clothing and bed linen to prevent allergies and other health hazards.

Other commonly used materials such as vacuum cleaner dust bags, coffee filters and tea bags are not as suitable as they are not designed to be used on the human body.

Also, tea bags and coffee filters are meant for filtering out large particles and allow water through, making them unsuitable for masks.

National sailor Kenan Tan, 12, fashioned a mask out of a cotton handkerchief.

"I went grocery shopping a few days ago and saw that the masks were very expensive. I'm glad I learnt how to make a reusable one after watching some video tutorials online," he said.

Mr Tan Haur, 56, an arts educator at special needs schools, has been wearing masks made by his multi-disciplinary artist wife Loh Kit Mui, 53, for the past two years.

"I used to fall sick more frequently in the past, but a fabric mask a day helps me keep the doctor away," he said. He wears a mask even when he is not sick.

Dr Teo cautioned though that DIY masks can provide only minimum protection against fluids, sprays or aerosols, and reduce the chances of an individual spreading his saliva droplets through the air.

Therefore, it is important that these masks are not used in medical settings or environments that involve fire, such as kitchens or food courts, as they do not have high flame resistance and may catch fire.

DIY masks are not comparable to surgical masks, he added, as surgical masks have three layers, with the outer layer being leakproof and the middle filtering layer normally being electretised to achieve higher filtration efficacy while maintaining good breathing capability.

Surgical masks typically have a bacterial filtration efficacy of 95 per cent and above. This decreases with use.

Dr Teo said mask wearers are also likely to talk less, which reduces the spread of their droplets and particles.

The wearer should also breathe in less through the mouth and more through the nose.