It will make it lok new, without washing it. If you have access to an air compressor, spray it full blast up close and it will clean it deep down. I use mine to clean the insides of all sorts of delicate video game stuff, electronics, etc. Works great on cloth.
I used to do this to a washable air filter and I never made the connection to the VB visor… 😛
Like the manual says, that’s not a good idea… I can’t remember if I ever washed mine (I’m not big on reading manuals :-P) but it started peeling around the edges at some point. I’m planning to make a couple new ones out of thicker foam–like the prototype ones are always shown with.