These are the big ones that look like they belong in a supersize pool. These are really great for a variety of exercises especially working on the abs and legs. You can get them for less than $20 at places like Walmart, Kmart, etc...Personally, I would not go through a workout without using one of these at least two or three times. I know that for some people they look cumbersome or they are afraid to look silly especially in a gym, but it is so important to get over that and give them a try. You can find many exercises for them both in magazines and online.