Medium that look like cotton??

Hey everyone,

Im trying to descide on what grow medium to use and I think I want to go with a combination of Rockwool and that cotton lookin stuff.

DOES ANYONE KNOW WHAT THAT STUFF IS CALLED ITS WHITE AND LOOKS JUST LIKE COTTON

CAN SOMEONE SEND ME SOME PICTURES OF IT IN ACTION AND THE NAME OF IT OR WHERE TO BUY?

Looks like cotton? I'd say either rock wool, vermiculite, or pearlite.