Luffa?
 

Has anyone experimented with using cubes of luffa sponge as a replacement for rockwool cubes to start their seeds?

yes i have but i did not use cubes of luffa. what is the purpose of cubes luffa???

Naviras is correct, there are alternatives to using rockwool, etc which cost a LOT less in the long run.

We were testing using regular sponge based materials, that germinated perfectly, and the materials to make several thousand cubes was under $35. However, the ability for someone to produce or grow their own luffa sponge would make the system that much more all encompassing. Essentially growing another integral part of his overall medium.