Smitty Two writes:

With a PLEATED filter, DOUBLING the thickness increases the SURFACE AREA by
about DOUBLE. So, you're actually DOUBLING the SURFACE AREA of the filter,
which effectively HALVES the air flow through each SQUARE FOOT of filter
material. Thus, PERMITS mroe air flow with LESS restriction.

Halving the air flow through each square foot, and doubling the square
feet, does not equate to more air flow, or to less restriction. You
better use one of your lifelines.

It's the same amount of total air flow. A reasonable measure of
restriction is pressure drop across the filter, and with half the air
flow per unit area, the pressure drop will be less.

How do you measure restriction, such that it would remain the same with
half the flow per unit area?

Dave