ya, that's a water bag, i've hit them but I've always thought they were just kind of gimmicy, you know, "the human body is 99 percent agua" I have one but never used it, it's in it's box. I have a 150 pound bag I use, it's common for bags to be 70-100-150 punds and made out of either canvas, vinyl or leather. Leather is the best and reacts the best to your punches and give you a good snap. Bruce lee used to have all kinds of bags, some filled with, i think, corn or beans or something really hard, he even had a huge bag that weighed like 300 pounds or more. Bags are indespensable but I've often found myself wondering about a new way for punching, some of the latest stuff looks fairly good, the fixed mitt machines. One major problem with bags is that you can't use them everywhere, if you travel, you can't set it up in your hotel room, if you live in an apt, you can't set it up there either.