N95 and Surgical Face Masks Effectiveness Against Viral Infections

During this COVID19 pandemic, proper face masks are difficult to find or outrageously expensive.

So why not make your own? As I embarked on my journey to make face masks to donate to health care providers, I wanted to know how much protection face masks actually provide against respiratory viral infections, (part 1), which videos on YouTube make the best masks (part 2), and how to sanitize and reuse a mask (part 3).


There are 2 interesting distinctions when it comes to masks: the particulate size rating does not necessarily mean the same level of protection against respiratory viral illnesses. The mask you chose must depend on its intended purpose.

Let’s start with particulate size.

The particulate size rating is very useful. When looking for a mask to protect you from smog or allergies, you want a mask that is rated for 0.3 microns particles. You don’t really need a mask that is rated better than that because 0.3 microns sized particles are the hardest particles to capture. Why is that?

Particles that are either larger or smaller than 0.3 microns are in fact easily captured by a 0.3 micron filter. This may sound counter intuitive especially when you think of the example catching a basketball vs catching a ping pong ball with a net which has holes nearly the size of a basketball. A net with holes that are just slightly smaller than a basketball will unlikely to catch a ping pong ball.

But the physics of motion changes when we get down to micron size particles.

Particles smaller than 0.3 microns have more Brownian motion. At room temperature, these tiny particles bounce around randomly. They don’t travel in a straight line. So these particles literally are bouncing “off the walls”. The smaller the particle, the more bouncing. Eventually they will hit a fiber and stick to it. For this to be true though, the net must be rated for 0.3 micron particles.

Corona virus is 0.1 microns in size. It has Brownian motion. It can be captured in a
0.3 micron rated filter.

Let’s look at rate transmission of respiratory viral illnesses for N95 and surgical face masks.

Surgical (medical) masks are not designed for use as particulate respirators and do not provide as much respiratory protection as an N95 respirator. N95 masks are designs to filter at least 95% of inhaled air of 0.3 microns sized particles. Most surgical masks do not effectively filter tiny particles from the air and do not prevent leakage around the edge of the mask when the user inhales or exhales. Not all “surgical” masks are rated by the ASTM rating system either. If they are not certified, their performance is unpredictable. Then there is the NIOSH rating system used by N95 masks. The number represents the percentage of the air being filtered. Many “N95” masks on the market are fakes, claiming to be N95 but not up to NIOSH standards.

Do not wear masks with valve

Many people are wearing N95 masks with an exhalation valve. These valves makes it easier to breath and more comfortable. Useful if you are jogging down a busy city street but somewhat useless if you want to stop a pandemic. If you should have a contagious respiratory infection, the exhalation valve allows unfiltered air to escape that could infect another person. If you have a choice, during a pandemic, don’t use a mask with a valve.


The infection rate in studies of influenzas and Corona Viruses (not Covid19) comparing N95 masks vs medical masks were not significantly different: 8.2% vs 7.2%. Currently we have to extrapolate and assume this likely applies to Covid19.

Wearing a mask only provides partial protecting. Multiple other factors are involved in contracting this highly contagious Covid19. Are you practicing Social Distancing? How physically close were you to the infected person? Did they have on a mask? Did you have on a mask? For how long were you with this person? What surfaces did you touch? How good is your health? Do you have any chronic conditions? Could you be taking better care of yourself? What are the barriers do you have that prevent you from taking better care of yourself?

Now we know that the more comfortable surgical/medical face masks perform as well as N95 in the real world against respiratory viral infections. N95 masks are uncomfortable to wear because of increase air resistance and the tighter fit against your face. Because of this discomfort, most people cannot wear an N95 masks for a long period of time.

Ideally, if we ALL, that is 100% of us wore a face mask for 2 weeks and practiced correct hand hygiene, this pandemic could come to a halt. Universal mask precautions. Assume everyone is infected with Covid19.

In Part 2, I will examine how to make a homemade surgical grade mask from household materials.


This blog is in no way meant to give any medical advice, diagnosis or treat. 

Everyone’s situation is different.

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