material

Has anyone use Polyfiber batting material in there HOB filters rather than the cartridges? I've heard that the batting is also an excellent media and is actually a little thicker, more effective, less expensive and lasts significantly longer. If so, do you still actually need the carbon or...

I've seen references to "egg crate" sold at Home Depot, to set under the gravel as a scaffolding for rock piles and for use as a tank divider. Which section of the store would I find this stuff in? What's it's non fish use. (I'm not what you would call handy around the house.)