sand, rock's{there's 1000's of kinds}, cotton, crushed glass, bark, cardboard, sawdust, crushed coral, the list go's on it all on your style of growing....
LOL....if you can find a way to secure the plant to the tub/bucket you dont even need a netpot...
wild mahn....my first DWC i just tie-wired the plants to the side of the crate i had..
(crate, lined with a thick platic bag and styrofoam for the lid, bubler and a overflow )
I just stuffed a plant in each corner and Bob's you unckle.....
400 w...Boom, Buds
All depends on the setup. You can pretty much use any of the materials mentioned above, but first you need to find out what type system you want to use so you can choose the optimal medium. (if needed) If you can get Lava Rocks, those should work just fine. You can re-use them as well.
sand, rock's{there's 1000's of kinds}, cotton, crushed glass, bark, cardboard, sawdust, crushed coral, the list go's on it all on your style of growing....
Sand, decomposed granite (pea gravel) lava rock, perlite/vermiculite mix, diatomite rock, really anything! These are just very common substrates used in hydro.