It's a Nylon screen that is removable, so it can be rinsed out and reused endlessly. The number of uses between cleanings depends upon how much debris there is in the water you are filtering. Just to clarify for everyone, the blue part is not a drinking spout, it is an air vent. This cap is only made for filling water bottles, not for drinking out of them.

Not a dumb question perfectly fine... The filter should last a very long time. You really cant put a finite time frame on it. It is analgous to a metal coffee filter that you use over and over again. Really as long as you clean it from buildup and dont break the micron screen this will outlast most of your other gear