Or, it's also called "bubble hash". Bubble Bags can be bought off Ebay,(60 for a decent set of 'off-brand', and about $250 for the real Bubble Bags. Both work great, but I'm guessing that the real bags are higher-quality, and last longer. It's one of the simplest ways to make great hash, even if you're just learning how to do it. Check 'em out.