ya the reason is dry kief has small particles of leaf in it. Because its dry its impossible just to get resin heads. Very small pieces of plant matter fall threw the screen and this makes the kief not stik together.. Bubble hash is wayyyyy purer. Just resin, so it sticks to itself with little pressure. The only reason they press kief and heat it up is to make the resin stick to the green, and then that green sticks to more resin and so on. Its only presed to keep it from falling together. Like japan said. Pressing hash will pop the resin heads and it will loose its flavore FAST! Trust me i know from experience. Pressed an ounce of hash together, and after 1 week and only smoking 7 grams, and the stuff went stale.. lost all its wounderfull flavors.