Best for hard to capture particles like soapstone and eggshell, or when maximum efficiency in a single stage is deisired. For best results use as the second stage ( back ) with a standard filter. Because of the fine weave it's not easily cleaned and will require more frequent replacement. The filter works fine as a single stage but they are best used in pairs ( stacked ). Adding an extra filter will increase the performance and life of the filter with no drop in suction.