N95 masks are also known as filtering facepiece respirators. These masks can filter out at least 95% of airborne particles. N95 masks are considered the gold standard of face masks in some industries and are often used by healthcare workers to prevent transmission of infectious diseases, pathogens, and other dangerous particles.

N95 masks fit snugly to create a seal on the face. They use trap aerosols and droplets in their fibers so the particles cannot enter the nose or mouth of the mask wearer. When N95 masks are worn correctly in a tight fitting manner, no outside air is able to enter on the sides of the mask, or from the person wearing the mask. This helps prevent the spread of COVID-19 to and from people correctly wearing N95 masks.

Most N95 masks are made of a material called polypropylene; a synthetic plastic fiber made out of fossil fuels like oil. This fiber is similar to ones found in clothing like rain jackets, yoga pants, and stretchy fabric. Polypropylene is also used to make looser fitting surgical masks, but these masks are not as good at filtering particles as N95 masks.

To make the polypropylene filters, thousands of nonwoven fibers are melted together in a process called 'melt blow extrusion.' Each fiber is thinner than a strand of hair. Each thread passes through a hole on a machine to create a layer of fibers that has the consistency of cotton candy. Hot air is then applied to the masks, which fuses the fibers together tightly enough that 95% of microbes can't get through, but air still can. The result of this process is a web-like filter that is often given an electrostatic charge that makes them even more efficient. In one recent study, adding this electrostatic charge to masks helped filter out even more tiny microbes than non-electrostatic masks by 10 times.

Besides the filter material, N95 masks can also include other materials, such as aluminum, polyurethane, steel, and, rubber. The company 3M uses a matter called polyisoprene to make fabric straps for their N95 masks. As N95 ratings mean a mask can capture 95% of particles, it does not mean the masks must be made with any particular materials, as long as it filters at that level. That means theoretically, N95 masks can be made from many materials but most masks approved by national public health agencies or procured/evaluated by the World Health Organization use polypropylene as the main material and filter.

N95 masks are not exposed to extreme heat when they are worn appropriately and are made by reputable companies whose ingredient lists have been evaluated by national and international health bodies. Due to the tightly fused polypropylene fibers in the mask, they are highly unlikely to shed fibers that can be ingested. If they do, it is very unlikely that enough fibers would be ingested to lead to eye or throat irritation, or digestive upset.

Polypropylene is considered safe for humans and is used widely in food and beverage products because of its ability to resist heat. This means the material can likely be exposed to warm or hot water and not leach any plastics.

However, N95 masks should not be heated on a stove, burned in a fire, placed in a microwave, or be exposed to extreme heat for any reason, including decontamination. Melting any plastic or plastic derivative can be dangerous, but N95 masks were not created to prevent or protect against extreme heat and temperatures.

Recent research showed that polypropylene may affect androgen hormones or cause a toxic response, but N95 masks do not pose a major concern. The fibers do not move within or from the mask, nor are they exposed to high heats when being worn.

In order to ensure N95 masks are safe and made with safety tested products, the World Health Organization notes that N95 respirators should be at least as protective as "United States National Institute for Occupational Safety and Health-certified N95, N99, US Food and Drug Administration surgical N95, European Union standard FFP2 or FFP3, or equivalent." The Competition Bureau of Canada notes that masks should be labeled with fiber compositions in percentages, seller's names and principal places of business, and other identifying information or national approvals. COVID-19 has caused a surge of counterfeit masks to be created whose content lists may be undisclosed. Purchasing N95 masks that do not disclose the above information or have appropriate vendors or markings to indicate national health agency approvals is not recommended.

In 1995, Peter Tsai and his team invented the N95 mask filter. Since that time the respirator has been duplicated and reimagined by dozens of companies, but every country holds different standards for their protective personal equipment.

For instance, outside of the United States, different criteria are used to evaluate efficiency, flow rate, and pressure drop of each mask. In the European Union FFP2 respirators are required to filter at least 94% of particles. KN95 respirators in China must meet at least 95% filtration (though some masks sold globally as KN95s do not meet this standard). In place of the N95 designation, Australia uses P2 or P3 masks, Japan uses DS/DL2 and DS/DL3, and Mexico uses a variety of masks ranging from N95s to R95s and P95 as alternatives.

Masks which use filtration rates of 95% or above and are approved by national and international health bodies are recommended for health care workers to prevent the transmission of COVID-19. Due to the global shortage of the masks and the supplies required to make them, N95s are not suggested for non-healthcare workers at this time. Instead, wearing a cloth mask over a surgical mask is recommended.