Mask FAQ: What is 'filtration capability'? Which reusable masks are safe to wear?

SINGAPORE - With more transmissible Covid-19 strains in the community and evidence showing that the virus can be transmitted through aerosols, people should be selecting masks with higher filtration capabilities.

The Straits Times looks at what this means and the types of masks that can offer sufficient protection.

Q: What does "higher filtration capability" mean?

A: A mask's filtration capability refers to how well it is able to filter respiratory droplets, which may contain bacteria or the Sars-Cov-2 virus, and prevent these from going through.

This is commonly measured by looking at the mask's particle filtration efficiency (PFE) and its bacterial filtration efficiency (BFE).

The PFE measures how well the mask is able to prevent aerosolised droplets - of around 0.1 micron in size - from escaping, while the BFE measures how effectively the mask can filter bacteria-containing droplets, which are about three microns in size.

The Sars-CoV-2 virus is said to be around 0.12 micron in size.

A good mask - which meets the requirements for medical and surgical standards - should have a BFE or PFE of at least 95 per cent, meaning that it is able to prevent 95 per cent of all such particles from going through.

Q: Which masks should I wear and which should I throw away?

A: You can wear surgical masks, or any of the masks given out by the People's Association or Temasek Foundation during the nationwide mask distribution exercises. These include the DET30 mask, the Proshield mask and the Livinguard mask.

Cloth masks that are made of at least two layers are also permissible.

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When buying surgical masks, it is important to ensure that they have been tested for either BFE or PFE against international standards, such as that set by standards organisation ASTM. This information can usually be found on the side of the surgical mask box.

You should stop wearing single-layered masks or masks with exhalation valves, as these do not have the same filtration capability or level of protection as double-layered and surgical masks.

A mask with an exhalation valve may be more comfortable and can be appropriate for haze, but there is a risk of aerosols and droplets escaping through the valve, especially when an infected person wearing the mask sneezes or coughs.

Q: What are reusable masks usually made of and what kind of material should I look out for when buying a reusable mask?

A: Most reusable masks are made of cloth.

When selecting a reusable mask, it is good to ensure that the outer layer is made of polyester, as it is a water-resistant material and can prevent droplets from entering the mask.

The inner layer of the mask should be made of a finely woven fabric, so that it is able to prevent respiratory droplets from escaping.

Some masks, such as the Proshield mask given out by Temasek Foundation, also have an inner pocket for filter inserts. This can help to improve the filtration efficiency of the mask.

Q: How often should I wash my masks?

A: You should wash your masks once a day after use to ensure that microbes from the skin do not remain trapped on them.

Hand-wash your mask using a gentle soap and lukewarm water solution, and avoid antiseptic detergent or bleach.

It is also important to take note of the lifespan of reusable masks, as such masks have to be replaced once they are used and washed beyond the recommended number of times.

This is because, beyond that, the filtration capability or antibacterial quality of the mask may not be as effective as before, especially if the material has been stretched or loosened over time.

For instance, the Livinguard masks given out by Temasek has two layers of treated cotton fabric that has antiviral and antibacterial properties.

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However, the antiviral and antibacterial performance of the mask will be gradually reduced after 30 washes.

This mask needs to be washed only once a week, and if worn daily and washed weekly 30 times, it can be used daily for about seven months.

You can also wash the mask daily if you wish, but its lifespan will then be much shorter.

Q: With variants of the virus circulating, do I need to double-mask?

A: No, it is not necessary, as long as you already have a good quality mask that properly covers your nose and mouth.

When going to more enclosed or crowded areas, it would be a good idea to select a surgical mask or a double-layered cloth mask with filter inserts for better protection.

Ensure that you are with no more than one other person, and go out only for essential activities.

This article was first published in The Straits Times. Permission required for reproduction.