N95 vs N99 vs Cloth Mask: Which Mask Actually Works Against Air Pollution

What do N95 and N99 mean?

The labels come from the US safety agency NIOSH, which certifies masks called "filtering facepiece respirators":

• N95: filters at least 95% of airborne particles of the size that is hardest to catch (about 0.3 microns).
• N99: at least 99%.
• N100: at least 99.97%.
• The "N" means "not resistant to oil", which does not matter for city smog.

India's standard, IS 9473 from the Bureau of Indian Standards, uses classes called FFP1, FFP2 and FFP3. FFP2 is broadly comparable to N95, and FFP3 to N99. Europe uses the same FFP classes.

Why cloth and surgical masks fall short

Pollution's most dangerous particles, PM2.5, are about thirty times thinner than a human hair. Cloth weaves have gaps far larger than that, and most cloth masks fit loosely.

A review of studies published in a medical journal found big differences in real-world performance:

• Cloth masks filtered between 15% and 57% of diesel exhaust particles in one test.
• A surgical mask filtered about 79%, but loose edges let unfiltered air in.
• Inward leakage, air sneaking around the edges, was about 9% for a fitted N95, compared with 22% to 35% for other masks in one study.

The same review noted that the health benefit of masks for the general public against pollution has not been directly measured. Masks reduce exposure; they do not make bad air safe.

Fit is everything

Even the best filter fails if air goes around it. Check every time you put it on:

1. Choose the right size. Many brands sell small, medium and large.
2. Both straps should go around your head, not just your ears, for a firmer seal. Many Indian masks use ear loops; pick ones with a clip that joins them behind the head if you can.
3. Pinch the nose clip firmly so it follows the shape of your nose.
4. Seal check: cover the mask with your hands and breathe out sharply. If you feel air escaping at the edges, adjust it.
5. Beards and stubble break the seal. Clean-shaven skin gives the best fit.

If your glasses fog up, air is escaping from the top: press the nose clip again.

N95 or N99: which should you buy?

• For most people on most days: an N95/FFP2. It is easier to breathe through for a walk, a commute or a day at work.
• For heavy exposure: traffic police, delivery riders, construction workers and people on long two-wheeler commutes might prefer N99/FFP3 on Very Poor and Severe days.
• For running and exercise: do not exercise hard outdoors on bad days. Any good mask makes heavy breathing harder; move workouts indoors instead.

Masks with valves

Masks with an exhalation valve are more comfortable because breath leaves easily. They protect the wearer from pollution just as well. The valve only matters for infection control, because it lets your breath out unfiltered.

Children, older people and those with illness

• There are few certified N95s sized for small children. A loose adult mask does little. Children under two should not wear masks at all; keep them indoors on bad days instead.
• For older children, look for child-sized FFP2 masks and check the fit.
• People with heart or lung disease, or who are pregnant, should ask a doctor before wearing a tight mask for long periods, as it makes breathing slightly harder.

How to spot a fake

• Look for a certification marking printed on the mask itself: a NIOSH approval number (starting "TC-84A") for N95/N99, or BIS marking with IS 9473 and the FFP class.
• You can check NIOSH numbers on the agency's certified equipment list.
• Be wary of masks sold loose, without packaging, or with spelling mistakes on the print.
• "Anti-pollution" fashion masks with replaceable "carbon filters" are often not certified at all.

How long does a mask last?

Disposable N95s are designed for limited use. Replace one when it becomes damp, dirty, damaged or harder to breathe through, or when the straps lose their stretch. Do not wash it: water damages the electrically charged filter layer that traps fine particles. Store it in a clean paper bag between uses.

This article is for general information and is not medical advice.

Related reading

• Air Pollution in India Explained: AQI, GRAP, Stubble Burning and Your Health
• AQI Categories Explained: What to Do When the Air Is Poor, Very Poor or Severe
• Delhi Air Pollution Season: Masks and Air Purifiers