What materials can and should be used for holding your plant in a hydroponic system?

Bottom line is that even if you don’t use dirt most plants like to have some sort of medium for their roots to spread out in. There are loads of soil-less mixes out there. The ones I have read about usually use things like vermiculite, sphagnum peat, and clay pellets.

Cotton material is probably perlite. Small gravel works also.

There are lots of growing mediums for hydroponics. There’s clay pellets and pea stones, coconut coir, perlite and a host of others. Important to remember: does not add to / change chemical makeup of the nutrient solution, porous, light, and coarse, allows oxygen and nutrients to easily reach plants roots.