“Should I buy the most expensive filter I can find?”
What MERV means
MERV is Minimum Efficiency Reporting Value — a scale describing what fraction of particles in given size ranges a filter captures. Higher numbers capture smaller particles and capture more of them.
A typical one-inch throwaway filter sits low on the scale. Media filters several inches deep sit considerably higher, and higher still gets into the territory hospitals use.
The part the packaging leaves out
Every filter is a restriction. A denser filter is a bigger restriction, and the resistance shows up as static pressure. Fit a high-MERV filter into a slot sized for a thin one and the system can lose enough airflow to undo the benefit — colder coils, longer cycles, and less total air moved through the filter in the first place.
The filter that cleans the most air is not the densest one. It is the one that captures well while still letting the system breathe.
Depth is the usual answer
The way out of the trade-off is surface area. A four- or five-inch media cabinet has far more filter area than a one-inch slot, so it can run a higher MERV at a lower pressure drop than a thin filter of the same rating.
That is a ductwork and cabinet change, not a shopping decision — which is why it is worth measuring before buying.
How to tell what your system can take
Measure the pressure drop across the filter you have now, and the total external static pressure of the system. Those two numbers say how much headroom exists.
Whole-house filtration, including hospital-grade filtration, is a real option — but sizing it against measured pressure is what separates it from an expensive restriction.