Doulton Ultra Sterasyl® Ceramic Water Filter Candle

“Absolute” and “Nominal” refer to different ways of stating the filter’s pore size and efficiency:
Absolute Rating:
– The absolute rating specifies the largest particle size that the filter will allow to pass through 100% of the time.
– For a 0.9 micron absolute rating, this means the filter will remove 100% of particles larger than 0.9 microns.
– No particles larger than the absolute pore size rating can pass through the filter.

Nominal Rating: 
– The nominal rating refers to the approximate particle size that the filter can remove with a specified efficiency, usually 85% or higher.
– For a 0.5 micron nominal efficiency of 99.9%, it means the filter removes 99.9% of particles 0.5 microns and larger.
– However, some particles larger than 0.5 microns may still pass through the filter, unlike the absolute rating.

The absolute rating guarantees 100% removal of particles above that size. The nominal rating indicates the approximate size removed at a high but not 100% efficiency.
The 0.9 micron absolute and 0.5 micron 99.9% nominal ratings show the Sterasyl filter has very high particle and microorganism removal capabilities down to the 0.5 micron range.