Ferrites are powdered molded metal powders cast into various shapes and sizes. Ferrites are actually a type of molded ceramic. They are usually made of powdered Iron Oxide (Fe2O3), along with Zinc, Copper, Zinc, and other metal oxides. The EMI portion of the filtered spectrum is converted to heat within the ferrite core and dissipated.
We sell the snap-on chokes, which can be simply opened up and snapped around the wires or cables. You can stack as many as you want and stack different types if you have severe problems. You don't need one for each wire unless you have really fat wires - they work just as well if snapped onto a pair or bundle of wires. They are non-conductive so can be used almost anywhere, including on 115-volt power lines and battery or inverter cables.