While filter ratings are an important indication of how well the filter will remove particles of varying sizes from a fluid or gas, it is important to note that nominally rated filters from different manufacturers can have the same rating, but yield different results. The opposite is also true – nominally rated filters from different suppliers can have different ratings, yet yield the same result. Naturally, this can create confusion and impact your filter buying decisions. When these situations arise, we recommend that focusing on achieving the targeted performance of a filter over the rating will yield the best results. With that in mind, let’s start with differentiating between the two types of ratings that indicate pore size and efficiency in removing particulates -- Nominal and Absolute ratings.