Originally Posted by Penguin
Just make the walls out of a printed spandex or other flexable fabric with a photography of a wall or brick or whatever printed on it (they can do it). Now you have many vertical slits in it, so it will be invisible but a bb will most always find a way through to the other side. After this, the slits would automatically close up and save you from having to replace a billion walls.
The only problem with that, is that it's not too sturdy for someone to bump in to, I'd rather have solid walls that can take a body check, than have my bbs be able to go through them....