Abstract: An object of the present disclosure is to provide a filter medium for an air filter which does not contain a PFAS nor a siloxane compound and has a good physical property balance among the PF value, the water repellency, and the strength. A filter medium for an air filter according to the present disclosure is a filter medium for an air filter composed of a wet-laid nonwoven fabric, wherein the filter medium for an air filter contains a binder resin and a water repellent, the water repellent contains, as a main component, a hydrocarbon-based polymer free of fluorine and silicon in a molecule thereof, and the binder resin and the water repellent are crosslinked by an isocyanate crosslinking component.

Abstract: An object of the present disclosure is to provide a filter medium for air filters that has a high PF value and high water repellency in addition to stiffness and strength that are practically sufficient, and to provide the filter medium with an easy production method. The filter medium, composed of a wet-laid nonwoven fabric including a glass fiber, for air filters according to the present disclosure includes a cationic binder resin, a fluororesin, and a cationic surfactant, and the solid content mass ratio of the fluororesin to the cationic surfactant is within a range of 30/70 to 80/20.