The trick is that the middle layer of N95 masks is an electret, a material that will hold an electric charge. It's the electrostatic equivalent of a permanent magnet. It's not a very strong charge, but it's enough to pull particles a few microns out of line and catch them in the filter.[1]

It's a mini version of an electrostatic precipitator, which has a coarse charged mesh and a strong charge. Those are good for pulling particles out of air.

If you want to test this, there are standard "fit test kits" for respirators. They're little packets of scented smoke particles. You put on the mask, break the ampule to let the smoke out, and if you can smell it, the respirator isn't working, or, more likely, is leaking.

[1] https://youtu.be/426IpWoEQsc