Frequently Asked Questions

Both KN95 and N95 masks filtration are tested to filter at least 95% of particles that are 0.3 micron in size.  The difference is this test is performed at different flow rates.  Most NIOSH-approved N95 respirators will have two headband straps, not ear loops. However, a few NIOSH-approved models are approved with ear loops because the loops are secured behind the head with a non-removable fastener.  Delve a little deeper

Filtration is only one aspect of a good N95 mask.  NIOSH requires the mask can seal to the face without leaks.  There are three masks, in particular, designed to improve the ability to seal to the face.  There are 3 masks with seals designed to improve the fit:  SoftSeal, Envo and the 3M Elastomeric mask. Delve a little deeper

The labeling on a mask is key to identifying NIOSH-approved N95 masks. A NIOSH approved N95 mask will have the NIOSH approval number (beginning with “TC” and following by the NIOSH number) printed on the front of the mask along with lot and model numbers. You can verify that your mask is NIOSH approved by checking this NIOSH website.  Delve a little deeper

The CDC recently released a statement on the use of N95 masks with valves. These CDC guidelines accept N95 masks with valves to be as safe as surgical masks, which everyone accepts as protective. While the CDC has changed its position on masks with valve, it may take time for the airlines and governments to catch up with current CDC guidelines, and therefore you should be prepared for push back if you wear a mask with a valve.  Delve a little deeper

NIOSH stands for the National Institute of Occupational Safety and Health and is a division of the CDC. NIOSH is responsible for N95 mask approval and certifies that N95 masks can filter at least 95% of particles in the 0.3 micron range (up to 5% of the particles get through the mask). N95 masks are also called N95 respirators. Note that there are also N99 and N100 masks with higher filtration, but also with higher resistance to breathing. 

Filtration of particles is not linear.  N95 masks are very efficient at filtering very small particles and very large particles.  The most difficult size particle to filter is around 0.3 microns in size.  Viruses are much smaller than 0.3 microns.  Very small particles “vibrate” in the air and get caught in mask fibers due to the vibration and/or an electrostatic charge.  Viruses also may be carried in much larger particles than 0.3 micron such as exhaled moisture droplets.  Delve a little deeper

A key component of maintaining a tight seal of N95 masks against the face is the tension applied by the straps that hold the mask in place. A head strap that goes around the back of the head is in a somewhat fixed position, as the skull does not change size. However, when a mask is held in place by ear loops around the ears, movement of the ears or the position of the ear loops on the ears, can change the seal against the face, and therefore break the seal, exposing the breathing zone to harmful particles. Therefore, NIOSH only approves masks with head straps or with ear loops that have a fixed connector between the loops behind the head. Masks that have separate ear loops and claim to be N95 masks are counterfeit and should not be purchased.

KN95 masks are expected to be tested against the Chinese GB2626-2006 standard for personnel protective equipment. This standard is very close, but not identical to the NIOSH N95 standard. However, as stated previously, they are not tested by a government laboratory in China and therefore, leaves open the potential for exporting masks that fail this standard. The Emergency Care Research Institute (USA) tested Chinese KN95 masks and found that up to 70% of masks tested by them do not meet minimum standards. Extreme care needs to be used when purchasing KN95 masks.

A fit test is used to determine if a mask provides the 95% filtration protection for a given individual. Wearers of N95 masks are either exposed to aerosols with a chemical they can taste if the particles get around the edges of the mask (the wearer tells the operator if they can taste the chemical) or particles that are measured inside the mask with a particle counter, calculating the protection of the facial seal. Fit tests are critical for individuals working in high risk environments where exposure to particles can cause significant disease or harm

Wearing an N95 mask with a good seal against the face is difficult for some people.  One reason for the difficulty is caused by the increased resistance for inspiring and exhaling air.  This resistance makes the person’s diaphragm work harder.  In people with impaired breathing to start, this resistance may be too high with any exertion.  The valve in an N95 mask is a one-way valve.  It closes when the person breaths in and opens when the person exhales.   It therefore protects the person from breathing in unfiltered air and reduces the resistance of breathing out.  This lowered exhaled resistance helps in reducing the work of the diaphragm enabling people to either wear a mask for longer periods of time without tiring and, in some, allow a mask to be worn at all. 

A second difficulty the valve helps with is the buildup of moisture in the mask.  An N95 mask with a good seal against the face traps moisture in the mask.  This can cause the person discomfort.  The one-way valve allows the exhaled moisture of the breath to be released from the mask greatly improving the comfort of wearing a mask for any period of time.

Valves on masks are one way. They allow the wearer to exhale through the valve so not all of their air has to exit through the higher resistance of the filter material. This makes breathing out easier. However, on inhalation, they close tightly, and all air is inhaled through the filter material, protecting the wearer from particles in their environment. The other advantage of valves on masks, is that exhaled air is 100% saturated with humidity. Without a valve, most of that humidity (and heat) are captured inside the mask. The valve allows some of this heat and humidity to escape through the valve, making the mask more comfortable to wear.

While the valve does allow some particles in the exhaled breath to escape, the CDC data suggests that while not as good as a mask without a valve, they are as good as a surgical mask as a source control for protecting others.

Most N95 masks are not sterile products and therefore, do not undergo any sterilization. They are however, produced in special “clean rooms” that meet the NIOSH required ISO 8 (US FED STD 209E Class 100,000) Clean Room standards. These rooms are sealed from the outside and have high air filtration systems to protect the product from contaminants in the outside air during manufacturing. All N95 manufacturing facilities are inspected by NIOSH on a regular basis to assure that manufacturing is done according to these requirements.

Yes, check out our Mask Pros & Cons page.

As a starting point, NIOSH does not have a requirement for an expiration date on N95 masks. Stored in their original packaging, the filtering material in most N95 masks should retain their NIOSH required filtering efficiency for at least 7 to 15 years.

In 2020, the National Institute for Occupational Safety and Health (NIOSH) reported a study of the “Inhalation and Exhalation Resistance and Filtration Performance of Stockpiled Air-Purifying Respirators: Overall Performance of Nearly 4,000 Respirators Sampled from Ten Stockpile Facilities”. It found that 98% of the air-purifying respirators tested from ten stockpile facilities and manufactured between 2003-2013 maintained their inhalation and exhalation resistance and filtration performance in accordance with NIOSH performance standards. This supports the expectation that N95 masks, if stored in their original packaging will last a long time.

However, there are two components that may deteriorate, depending on their material. Over time, and particularly when exposed to heat, some head straps may lose their elasticity. This can reduce the ability to keep an effective seal against the face, reducing its protection. Some head strap materials are less susceptible to heat and storage on their elasticity and will remain effective for 15 years, particularly if they have a tensioning adjustment. The other component that can prematurely fail is the valve on N95 masks that have one. Some masks use a rubber flap valve that can dry out and either crack or lose their ability to seal, allowing inward air leakage and particle ingress. Valves produced from silicone can last more than two decades and still retain their structure and performance.

So why do some masks have expiration dates?

Some masks have expiration dates because of the life-testing performed by the manufacturer where they found potential material failure over time. However, the predominant reason for the recent addition of expiration dates has been new laws written by the Chinese government. At the beginning of the pandemic, there was widespread shipments of fake N95 masks from China. In an effort to clamp down on these shipments that were giving China a bad name, China instituted tighter controls over the export of N95 masks.

One of these controls was the mandate for expiration dates on the masks, whether needed or not. In response, manufacturers were required to add an expiration date that did not reflect the actual time where the mask would still meet N95 filtration efficiency requirements. Manufacturers were then faced with picking an arbitrary shelf life. The difficulty with picking a shelf life is that if you pick one, you have to be able to prove it. So, most companies picked 3 or 5 years, a time period they were able to prove, even though their masks might perform for 15 years. 

My personal bias is to ignore the expiration date on masks unless it is more than 15 years old as long as it was stored in its original packaging. On masks used beyond their printed expiration date, you should check the tightness of the head straps and visually inspect the exhalation valve if it has one. If the straps hold the mask tight to your face and the valve seals, I would feel protected.