Don,
A lot of the stuffing is sort of a quilted cotton fiber.........probably similar to the stuff found in those cheap quilted lined jackets., mixed with some foam bits and other assorted cloth. Simple and stops em' dead........and I' m shooting carbon arrows in the 300fps/80+ ft lb of KE range.
Its an amazing target....and like Rack said pulling arrows is just silly. It makes even pulling arrows out of the Block feel like a chore, and there is absolutely no comparison to a reg. foam 3D target. You can' t shoot broadheads into it, but for field point shooting I don' t see how you can beat it.