Normal filters have multiple layers too - for example first you can have the screen that keeps the large particles out. Then you have the activated charcoal, and then the paper to keep the charcoal out, and for high-end filters you finish off with a porous membrane.

And yet, it's all one filter.

SO... we're speculating here on where the bulk of the work is being done. The strength could be evenly distributed from beginning to end, but it could also be lumpy.