ULPA is an acronym for "ultra-low penetration air". An ULPA filter can remove from the air at least 99.999% of dust, pollen, mold, bacteria and any airborne particles with a size of 120 nanometres (0.12 micron) or larger.
A number of recommended practices have been written on testing these filters including IEST-RP-CC001: HEPA and ULPA Filters, IEST-RP-CC007: Testing ULPA Filters, IEST-RP-CC022: Testing HEPA and ULPA Filter Media, and IEST-RP-CC034: HEPA and ULPA Filter Leak Tests.