How do N95 masks filter droplets and pathogenic particles?
What is an N95 mask? 

To be classified as an N95 mask, they need to meet certain criteria. This is defined by the National Institute for Occupational Safety and Health (NIOSH), an institute responsible for regulating personal protection equipment to prevent work-related illnesses or injuries in the United States. They are a part of the CDC and are a federal agency in the US. 

NIOSH has a rating classification for air filtration, in which respirators or masks are classified into different categories based on their filtration efficacy and other features. This rating gives respirators a name, which can be broken into two parts:

  • The letters N, R, or P: they indicate resistance to oil. The ‘N’ from N95 means these masks are not resistant to oil. This characteristic allows them to filtrate only non-base particles, like viruses.
  • A number: this represents the percentage of minimum filtration efficacy. N95 masks can filtrate at least 95% of all airborne particles in the air. 

These two properties are what make the N95 respirator a critical piece of PPE needed in many industries, especially the medical one, and this necessity has increased since the start of the pandemic. 

What are they made of?

N95 masks can vary in the materials they’re made of. For example, one of the most used materials for the mask is polypropylene. This is a thermoplastic polymer, meaning that it can be molded at a certain high temperature, and solidifies in that position after it cools down.

Polypropylene is a polymer of propylene, which is a monomer. If you don’t know what these words mean, don’t worry. This just means that polypropylene is a material made of a lot of propylene molecules. 

Propylene is a hydrocarbon, which means we can get this material from fossil molecules. This material is the second most used plastic in the world and is a big component of the textile industry. Yes, your clothes are probably made of polypropylene.

Polypropylene is a non-woven fabric. This means that it doesn’t need any weaving techniques to be used. The high use of this material in textiles is due to its light nature, and high resistance to many environmental threats, like abrasion, acid, and alkalis.

Other materials that can be found on N95 masks are metals like aluminum or steel. These are used for small details, like the nose clip or the staples.

It’s important to keep in mind that the term N95 mask comes from a certification by NIOSH, as we explained above. This classification comes from the performance of the mask, and has nothing to do with the materials. So, an N95 mask could be made of virtually anything, and as long as it meets the criteria, it will be considered an N95 mask still.

How they work 

N95 mask filters have a series of very small pores made to trap very small particles. Airborne particles have a standard diameter of 0.3 micrometers, so the size of the pores need to be able to trap particles that are that size for the mask to be certified as N95. Also, as we explained earlier, N95 masks are not resistant to oil, meaning that they are only effective to filter out particles that aren't oil-based. This is why N95 respirators are a suitable PPE for such fields as the medical, dental, or surgical ones, as it effectively filters out bioaerosols like viruses. But it is also used in other industries, like construction, mining, and those involving paint. 

However, the mask filtration mechanisms have to meet other requirements. A pore size that is too small can prevent the user from breathing correctly, so the pore diameter can’t be too small either. To optimize the filtration potential of the pores without reducing its diameter further, N95 masks have other types of filtration mechanisms, such as electrocharged filtration.

Polypropylene isn’t electrostatically charged naturally. But manufacturers can add these charges to the material to enhance its filtration potential. The principle behind this method is to employ electrocharged fibers to attract both large and small particles that are oppositely charged, and trap them. This, in addition to the mechanical filtration of the pores, ensures that all particles are being filtrated through the N95 mask.

What happens if you reuse? 

N95 masks are designed to be discarded after use. They are disposable face masks with a lifespan of about 8 to 12 hours of use. After that time, the N95 respirator loses its filtrating properties, and won’t be as effective as before.

This is due to the degradation of the materials found in the mask. Even though polypropylene is very resistant, it will start to lose its resistance after the defined lifespan. The material also loses these electrostatic charges with time.

However, the Centers for Disease Control and Prevention has a series of guidelines to prolong the lifespan of N95 respirators. This has come as a way to face the COVID-19 pandemic, to optimize our N95 mask supply, and prioritize its use by the health care workers at the frontline. 

So, under these strict rules and regulations, N95 masks can be reused, but there aren’t any substantial research results showing that sterilizing or cleaning them can help to extend their use. These procedures might damage the materials and prevent the mask from ensuring full safety.


We would like to recommend to our readers to stay safe and socially distanced. If you leave your house, make sure to protect you, your family, and your kids by wearing an N95 respirator. You can purchase them while they’re still in stock at any online store, where different models and sizes are currently for sale. 

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