I'm not 100% sure but I think mine is aluminum because it was a cheaper one at a head shop ($30) but the kief does stick everywhere on this thing. I usually use the little brush that came with my breard trimmer to brush it all down into the kief box. If I didnt do this it probably would get all sticky in the threads that screw the grinder peices together and it would be hard to open and close but I dont think it would ever be completly stuck shut.