A couple of years ago I wondered if a sponge could be used as a growing medium. Figuring that it was perhaps a little too 'sterile' I set about growing some moss on it. My U campbelliana had been multiplying well in a more traditional growing medium, which unfortunately started to succumb to a fungal attack, so I decided to remove it and transplant pieces into different growing mediums in the hope that at least one would survive. One of those mediums was the car cleaning sponge and much to my surprise this piece is performing best out of all the transplants:
In the pics below you can see a little bit of the sponge. It has a net covering it, which I believe is designed to help remove bugs when used to clean a car.