Thread by @paibangzhu

Looks like folks here are not familiar with it?

Let me try to explain in layman language then.

The cloth is called "free-fit lip" by Koken, or "face seal" by other manufacturers, but they are basically the same.

They are air-proof. 1/n

https://twitter.com/PolitWare/status/1748808481304400373

The first benefit.

Let's say you are wearing a 3M aura. It fits quite well. Everything is good.

But you might notice it's a bit less breathable than its test result indicates. Why?

You can paint your face in red color and don your aura. It'll look like this. 2/n

You'll need the part in red to fit, therefore you could no longer use them to filter.

The total area of filtration material is reduced when you put on your aura.

And Aura is even not the worst case. Look at this! 3/n

With face seals you'll barely lose any filtration area because your face just don't touch the filter. It'll thus significantly improve breathability.

Even better, now you also have more area to fit your face, which improves fit factor as well. 4/n

As you may notice, most face seals come together with plastic frames.

Those frames are pre-shaped. They'll help make sure the face seals are pressed onto your face with as little leak as possible.

They also stretch the filtration material so as to maximize breathability. 5/n

I guess it's Shigematsu that first invented the face seal + frame combination. It has become quite popular in East Asia now.

With a proper frame and face seal, you can achieve 200+ fit factor even in ear loops.

And the best part is breathability.

It could be as low as 40PA (well this one is still in development).