they make both an earseal kit and a earcup foam kit (called softseal and hushkit respectively if i remember correctly). the ear seals are really soft leather with memory foam as filling. very comfortable, my only complaint being that they get as hard as rock when they get cold and then it takes a pretty strong effort to get your melon into the helmet.
the hushkit cuts down on a lot of the reverberated noise in the hard earcups, its basically just some layers of foam that surround the headphone. ive been really happy with both, and i think the combo of the two kits cost me about $80 canadian (don't quote me on the price, it was a while ago).