121 < Cross-Platform >

A very thick, binder-free microfiber glass filter paper used in laboratories for fine particle retention.

While not a standard ISO size like A4, "121" appears in specific contexts: A very thick, binder-free microfiber glass filter paper

Midterm or exam papers for agriculture-related courses (e.g., Plant Pathology or Entomology). 4. Paper Dimensions A very thick