Ahlstrom Grade 26 is a binder-free microfiber glass filter made with acid-treated borosilicated glass microfibers with inherently low levels of barium and zinc.

It is then acid-washed using the 1N HNO₃, as described in the EPA Method 1311, and thoroughly rinsed in a multi-stage process using copious amounts of high-purity deionized water. The filter media contains no binders or other additives that may cause interference with samples. It is recommended for use in the Toxicity Characteristic Leaching Procedure (TCLP) as described in EPA Method 1311.