Product review (3 stars): Okay if used backwards.
The filter fits well on 16" fan (size of cage). However, when you put it on the front of the fan, it blocks the air flow. I tried it on the back of the fan where it gets really dirty especially when it is placed in front of a window. The elastic is stretchy enough that I could get the base of the fan and the cord through the opening. So I will see how clean it keeps the fan this summer.