its a cottony feeling material, that is sewed right to the ripstop tho,,,but I was super disappointed how the pillow just flattened when I laid my head on it to where I took all the down out of it, and added the down to a syntethic Coccoon black pillow I had,,making it 9.5 oz heavy and perfect for my head, neck and back,,as I have to use a pillow..and couldn't see packing that heavy a pillow..so I re-stuffed the black rock shell ,,first with 2 ozes and wasn't enough then another oz,,then finally a 4th oz,,and its firm as all get out and still compresses a dash when your head is on it,,and works just great for my head when on my side,,and weighes in at 5.3 oz. This pillow as cost me about 110 bucks,,but I like what I have.
That black rock pillow is total weight including the flap of material in a triangle and mitten hook at 2 oz,,so figure,,there is only a oz or maybe a little more of down in it? (and giving black rock the doubt) in it if that. I cut the mitten hook and triangle of excess material off it for my weight, with 4 oz of down, so figure the pillow material the shell is made of at 1.3 oz.