N95 masks made from synthetic plastic fibers are most common. These plastic fibers are similar to the fibers in synthetic and polyester shirts many people wear.
N95 Masks Made From Synthetic Plastic
For example, let’s take the 3M 9332 masks that I wear in Beijing. Technically this is an N99 (FFP3) mask, but the idea is the same.
3M makes the filter material in the 9332 mask using polypropylene fiber.
N95 Masks Made From This Raw Material
Polypropylene in the filter medium is a plastic. Manufacturers make this plastic out of fossil fuels like oil.
That means the fibers in these masks are similar to fibers ones in our clothes. Companies use these fibers to make clothes like quick-dry shirts, rain jackets, yoga pants, or any stretchy fabric.
Mask makers often give the polypropylene material a electrostatic charge. That static charges makes the filters more effective. 3M has a great video explaining how static charge works in masks:
N95 Masks Also Contain These Materials
Besides the filter material, N95 masks can also include other materials, such as metal. For example, the 3M 9502 (that Smart Air tested for decontamination in the microwave) contains several metal parts. The mask uses steel for the staples (which secure the straps to the mask) and aluminum for the bendable nose clip.
N95 Are Ratings, Not Materials
However, it is worth keeping in mind that N95 is a rating certification about performance, not materials. The N95 rating requires masks to capture 95% of particles. Thus, theoretically, N95 masks could be made out of any sort of material as long as they meet these requirements.
This chart explains exactly what’s required of masks to be certified as N95 in the US versus similar ratings in the EU, China, Australia, Korea, and Japan. Although there are differences on many aspects, none of the agencies require a specific mask material.