3-Filter-Set: This set is for the Ionpia H2 , which has triple ﬁltration. First filter - sediment filter; second filter - .01 micron (absolute) hollow membrane technology trapping microorganisms such as bacteria or cysts; and third filter - carbon block reducing chlorine and other contaminants.
2-Filter-Set: This set is for the original IonPia. It contains: Carbon Block and .01 Hollow Membrane filters.
If you're not sure which filter-set you need, open up your machine by removing the side panel on the right and look inside the machine.
The cost is the same, either way, but please do make sure you are ordering the correct filter set for your machine. Customer errors in ordering can lead to unnecessary extra shipping expenses (which fall on the customer to pay).