It is the best way to keep the portable air filter in front of you chest

Where to keep the portable air filter ?

Most of time you may keep the portable air filter on arm (by belt). But the filter will move down position after a while, and it is not good for the blood flow if the belt is too tight.

I found the best way is keep the air filter in front of your chest by name card rope. It is no heavy, and free for arm. 

You can try it.