Micron Ratings

When choosing a filter bag, understanding the difference between a nominal and an absolute micron rating is crucial for ensuring you get the performance your application requires. These ratings directly tell you how efficiently a filter can capture particles of a specific size.

For historical reasons, most liquid filter materials are assigned a nominal micron rating, which is based on an efficiency of 50% to 80%. This means a filter bag rated at 50 microns nominal will, on average, remove 50% to 80% of all particles larger than 50 microns in a single pass. While this can be a cost-effective solution for less-critical applications, the lower efficiency means a higher chance that some larger particles will pass through the filter.

For applications requiring higher precision, an absolute micron rating is what you need. A filter with an absolute rating is certified to capture a much higher percentage of particles—typically 90% to 98%—of its rated size in a single pass. This level of reliability is essential for processes where even a small number of larger contaminants could cause significant damage or product quality issues. Absolute ratings are generally displayed with the micron size followed by an "A," as shown in the table below, which represents the available micron ratings for our most popular filter media.

The filter media itself determines whether it can achieve an absolute rating. Multilayer microfiber filter media is one type that can be given an absolute rating due to its multilayer, gradient design. While Filterbag.com may not offer every possible combination of size and media type, Midwest Filter can manufacture them for you.

Please contact us with any questions about specific media types or for assistance in selecting the best filter for your application.