Our description:
Hydro Crunch expanded clay pebbles
1st they are unpackaged. Then we
. remove 50-ish layers of clay dust, rinse them ( your welcome) and repackage according to order. It comes in almost every kit we sell and will be noted if it isn’t.  
Also available in 12L,  24L
6” net lid = 1.5L +/-
Official description:
 
. This natural clay is mined, formed into pellets, then kiln fired at high temperatures to cause the clay to expand into tough, lightweight balls. Clay naturally has balanced capillary action, with an ideal surface structure. Hydroton brand expanded clay is semi-porous and generally does not float like other products can. For best results, rinse all expanded clay before use. It is reusable as long as it is thoroughly cleaned between uses.
Size specification is 8-16 mm.