SINGAPORE - The humble three-ply surgical mask has become the hottest commodity during the coronavirus outbreak, with many buying what they can get their hands on.

But experts warn that while masks may look the same, the quality can vary wildly.

A recent test conducted by The Sunday Times showed that some are, in fact, made of poor quality materials and may just be giving users a false sense of security.

Mr Winthrop Wong, director of Wellchem Pharmaceuticals, whose surgical masks are used by hospitals here, said that masks that go into Singapore's national stockpile would need to meet American and/or European standards in terms of breathability, bacteria-filtration efficacy, water-resistance, absorbency and non-flammability.

With Mr Wong's help, The Sunday Times conducted simple tests on six brands of masks available on the market here.

They are:

1. Ultraguard from Wellchem Pharmaceuticals: These are distributed from the national stockpile to hospitals.

2. Golden Gloves: A box of 50 was bought for $9..90 from ABC Bargain Centre at Bedok.

3. Sensi Mask: A box of 50 was bought for $10 from a street peddler in Jakarta, Indonesia.

4. No brand: A box of 50 mask was bought from a local medical supplier for $20.

5. No brand: A local taxi company distributed these blue masks to its drivers.

6. No brand: A local taxi company distributed these white masks to its drivers.

For a surgical mask to work, the outer-most layer should be water-resistant, and the middle layer, which is used to trap bacteria, should not be too porous.

The innermost layer has to be able to absorb moisture such as saliva, mucus and sneeze droplets.

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An absorbency test found that five of the six masks could not absorb any moisture. That means if the user sneezes, the mask will not be able to contain the droplets, which will remain smeared on the wearer's face. Absorbency is also an important factor for comfort, allowing the user to wear it for longer hours.

The only mask that passed the absorbency test is the one from the national stockpile.

When Mr Wong cut up the masks to examine the middle layer, he found at least two masks which looked porous, and one with an extremely thin filtration layer. A very thin layer would not be able to effectively trap bacteria and particles, he said.

"The whole idea of wearing a mask is to protect the people around you, not mainly to protect yourself. That's why our government says wear a mask if you are sick. So any germs can be caught inside the mask and you can throw the mask away," said Mr Wong.

For the flammability test, the white mask that was given to taxi drivers by a taxi company caught fire.

The outer layers of all six masks passed the water-resistance test. This is to help prevent contaminated droplets from others from being inhaled.