Behind the Mask

N95 Mask
The humble N95 Marks.

My dad is a mechanical engineer like me. And more than a theoretical person he is a practical man. He likes making things that he designed and test them to their limits. So yeah, my childhood was filled with awesome experiments and lots of dust. To carry on the tryouts, he and his sidekick (me, hello!) used a mask. This mask was usually an N95 mask, which now has become a new normal.

I used to think that the mask I'm using is like a strainer-filter. My mom loves drinking tea and she uses a strainer to filter out the tea seeds off the drink. I connected these dots and considered that the mask I'm using does the same. It filters off the particles bigger than the holes in the mesh. Thereby, letting the cleaner air through for my breathing. Boy how wrong I was!

Unmasking the history

Many of us didn’t know what an N95 Mask was before March 2020. It might be surprising to many that this mask dates back to 1910. Similar to today, there was an outbreak in 1910. The onset was of the Manchurian Plague. As necessity is the mother of invention, a Malaysian physician, Lien-teh Wu worked on public health leading to the first-ever face mask. It was the first-ever object that protected the users from the bacteria. Rigorous empirical testing showed positive results leading to overwhelming usage of face-mask in the 1918 flu pandemic.1

Earliest Face Mask
The face mask as designed by Lien-teh Wu.

The concept of having protection over the face in environments that can be harmful to humans, lead to a plethora of design changes and variations of the face mask. A considerable variation and demand were seen during World War I. The gas mask is the successor of the face mask which was used by miners in WWI. They were reusable but bulky and uncomfortable due to their fibreglass filters and heavy rubber construction. In the 1970s, the Bureau of Mines and NIOSH developed standards for single-use respirators, and the first N95 respirator was developed by 3M and approved in 1972. 3M used a melt blowing process that it had developed decades prior and used in products such as ready-made ribbon bows and bra cups. A designer, Sara Little Turnbull pioneered the usage of it in a wide array of products.

It was not until 1995 when a patent by a professor at the University of Tennessee, Peter Tsai made the design for a virus blocking mask which was so effective that we still use the same idea. The anti-viral technology was first developed to prevent the spread of drug-resistant tuberculosis.2 When I first understood how this mask worked, I could not help but appreciate the genius of it!

Between the Science

During my academic years, I developed an after-treatment device for diesel engines with my professor. During the study of the physics behind filtration, I came across four mechanisms. Now, to explain it, let's get into the basics. At first, as I said that I used to think the mask was similar to a strainer-filter. This strainer filter blocks out particles that are bigger than the holes in it. And to block out smaller particles, simply add many many layers of the filter. Simple? Not exactly. Don’t be surprised when I say that the N95 mask works well with big and very fine particles, but not with the medium-sized particles.

Airborne particles bulkier than the size of a thousandth of a millimetre will travel in a straight line because of their inertia. No, gravity will have a petite effect because of the scale. The mask is made more effective by adding many layers of the mesh. This stacking of layers guarantees the impact of the particles of this size to hit the fibres. This phenomenon is called "inertial impaction." These particles once stuck to the mesh, they will be there forever because of the Van der Waal forces. Particles smaller than this usually follow a random zig-zag pattern because of the collisions it has with air molecules. This motion is called the Brownian Motion. This motion makes it very easy to capture the particles. This phenomenon is called "capture by diffusion." Particles of in-between sizes (~0.3um) are the ones which are hardest to capture. The reason for this difficulty is that these particles don't usually travel in a straight line or bounce around. They follow the path that airstreams follow. The airflow is generally around the fibre threads so the particles miss them completely. But if they are captured then it is called "capture by interception."3

Filtration Mechanisms
Filtration mechanisms.

To solve this problem of these particle sizes the N95 mask has a brilliant trick up its sleeve. The threads attract the particles using an electric field. This phenomenon is called "capture by electrostatic attraction." In the presence of an electric field, neutral particles develop internal electric dipoles. This dipole polarity makes them attracted to the fibre. This is the same reason styrofoam gets stuck to cat fur. But unlike a cat, an N95 mask's electric field is not ordinary static electricity. They are given permanent electrical properties like magnets are magnetised. Similar to magnets, the strands get electrical properties by putting them in the electric field. By electretizing the fibres in an N95 mask, they gain a long-lasting ability to attract particles, which means they capture about ten times as many particles as traditional fibres. And this is, after all, the point of an N95 mask: filter out particles from the air. By taking advantage of the molecular scale stickiness of matter, using many layers of fibres that catch straight-moving large particles as well as zig-zagging small particles, and having an electric field that attracts all particles, you get a mask - not a strainer. And it is really good at trapping both small and large particles and does a reasonably good job at filtering out middle-sized particles. Precisely what fraction of those sneaky medium-sized particles gets blocked gives you the number of the mask. If the number is at least 95% of those particles are filtered out, then the mask is rated N95.

Life Is Healthcare

But if you are a healthcare worker wearing one of them, here are a few essential things to look out.

The considerable influence on the performance of an N95 mask is not the mask. It is whether you wear it properly. If a facemask is not sealed on your face, air (& particles you’re trying to filter) can bypass the filter entirely.

Dust, smoke, pollen, bacteria, and viruses all have different sizes, and so are filtered by N95 masks to contrasting extents. However, germs for airborne illnesses don’t usually travel on their own. We breathe or cough them out in droplets which have a wide range of sizes. So the size of the virus or bacteria itself isn’t particularly relevant.4

How to wear a mask
Key factors for a mask to be effective.

N95 masks are intended to be disposable, but the demand from COVID-19 has led to a global shortage of N95 masks and the reality is that health workers have to reuse them - and thus decontaminate them. It’s important to be aware that certain kinds of decontamination (for example, using alcohol or liquids) can damage the electrostatic properties of a mask and destroy their filtering ability, even if the mask appears visually unaffected.

It’s your turn now

There is a strength in a product when it is simple and, yet it solves humongous problems. The N95 mask is one of such products. As an engineer myself, I want to design something like this that will help humanity. Imagine the world before a normal face mask. How many people would've died because someone did not strain on public hygiene? I am really thankful to Lien Wein teh to come up with this simple design and solve the issue that was killing people. So we should be curious like him and see the problems around us that need solutions. Solutions like face masks, sanitizers, soaps and dispensers that solve issues no one has thought of. We can change the world with a simple idea.

It is one of my life goals to design something similar to this. Something that has a huge impact on human civilization. I hope I have inspired you to design something similar or appreciate things like this. If you can trust me with content that you will make you see things that are usually ignored, feel free to subscribe to the blog. Better yet, why don’t you follow the blog on social media? I have included the links below. Have you come across any such ingenious solution that MUST be featured here? Do write to me about them.

Have a good one. See you next Saturday!

  1. Reddit:r/theinvisiblegenius
  2. Instagram: @theinvisiblegenius
  3. Twitter: @notnitinchopra

Reference links

  1. The N95 mask: The untold origin story
  2. N95 Mask Shortage Brings Inventor Out Of Retirement In Search Of Safe Reuse Method : Coronavirus Live Updates : NPR
  3. Technology Review of Modern Gas Turbine Inlet Filtration Systems
  4. Proper N95 Respirator Use for Respiratory Protection Preparedness | | Blogs | CDC


  1. Never thought electrostatics is involved in a mask like this. Understood it in one read. The scientific insight will help in proper use of these masks (which we tend to sanitize) Great work!

    1. Thanks Sachid!
      Many more articles to come like this!

  2. A good, crisp and clear ten mins read. Nice comprehensive stuff Mr invisible genius.

    1. Thanks JB!
      I hope future articles will be as insightful as this one!

  3. This article is very good. I like it.Interesting post. Thanks for posting this.Please share more information

    Performance of N95 Respirators Mask

  4. Really I enjoy your site with effective and useful information. It is included very nice post with a lot of our resources.thanks for share. i enjoy this post. airborne sanitiser


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