During 1920, a plague broke out between a shared jurisdiction of China and Russia. The Chinese Imperial Court brought in a young doctor named Lien-teh Wu that determined that the plague was not spread by fleas but through the air. He expanded upon the surgery masks he'd seen in the West, and made it from gauze and cotton and added several layers of cloth to filter inhalations.

When the Spanish flu arrived in 1918, the mask was well-known among scientists and the public.

• At first, the masks wrapped around your entire head to clean the air supply.
• Similar masks, loaded with fiberglass filter, began to be used in the mining industry to prevent black lung. It could be washed and reused.
• Although it saved lives, it was burdensome, and the dangers of inhaling asbestos became known.
• In the 1970s, the first single-use "dust" respirator was created.

Instead of fiberglass, single-use respirators are made from melted polymer and air-blasted into layers of tiny fibers with bigger spaces between them.

As particles fly into this maze of fibers, they get stuck. An electrostatic charge is added to the material, so even smaller particles are pulled toward the fibers, while the big holes make it easy to breathe. The longer you wear an N95 respirator, the more efficient it becomes. But breathing becomes more difficult over time as the bigger holes get clogged up with particles.