SCNBox as bounding box

From the Xcode documentation I understand " For example, if you create a physics shape from an

SCNSphere

Now I am trying to create a bounding box, where particles inside are contained by the walls of the box. I had painstakingly constructed six individual walls to form such a box, but was hoping there is a parameter I missed that allows non-collisions inside an SCNBox and collisions as they try to leave the friendly confines.