I used marbles one time. Actually they work really well except
A) they're expensive
B) they tend to let light through them.
If i were to do it over again, I'd probably buy some dark or solid colored ones.

That's definitely one I haven't heard of before grizzman. I haven't used them myself, but I have read about some people using Polymer crystals.

What about gravel?
I have seen tyre Granules & plastic granules & beads as media.
In which sense you used the word "Strongest"? Do you want media that don't deforms after multiple use. If so gravel is one of them. As far as marbles is concerned as Grizzman stated & want to use them you can use very thin layer of Oasis floral foam over the top of media to avoid light penetration. I persoanlly hate media that interferes with pH levels & causes algae growth
such as Rock wool. Marbels or gravel or styrofoam will not interfere with pH & a thin oasis foam layer can be used in such case over the top. Can you be more specific about using "Strongest" media? By using havier media as gravel may interfere with ROOT growth too.
Cheers.

azee_2009

It's not "Strongest" (Having strength or power greater than average), but "strangest" (Being definitely out of the ordinary and unexpected). I'm just wondering what types of odd materials other people may have used as a growing media, and/or how it worked out. Rather than the traditional hydroponic growing medias.

I've considers the rubber mulch that's made from recycled tires as a growing media. Though I haven't wanted to try it because I'm concerned about to many chemicals leaching into the nutrient solution. The rubber mulch I've found is also reddish in color, and I was told the color leaches and will even stain cement. So I haven't really considered using it.