Thickness matters, but it is only one variable.
A thicker bag can still fail if the film has poor dispersion, weak seals, uneven thickness, or low tear resistance. A well-engineered thinner film may outperform a poorly manufactured thicker one.
I would evaluate:
- thickness distribution, not just average thickness;
- tensile strength in both directions;
- elongation;
- puncture resistance;
- tear propagation;
- bottom-seal strength;
- drop and load testing;
- storage aging;
- actual consumer use.
The most useful question is not "How many mils?" It is "Where does this bag usually fail, and has the design addressed that failure mode?"