This very thick grade offers finer particle retention than Ahlstrom 111 with high wet strength and loading capacity. Ahlstrom 121 is recommended for the clarification of liquid suspensions loaded with fine particulates. Ahlstrom 121 is also used in membrane pre-filtration and is also found in quantification of solids, and LSC (Liquid Scintillation Counting) techniques that require high loading capacity.

Standard glass microfiber filters contain no binders or other additives that may cause interference to sensitive enzymatic or other chemical reactions. The unique characteristics of glass microfiber filters make its use particularly advantageous to laboratory filtration by enabling fast filtration of large volumes and difficult solutions without premature clogging.