When I redid my ABG 24' round pool 8 yrs ago, I put 1" styrofoam down first, cut it to fit, qrey taped the seams. I thought it would be a cheaper alternative to "Happy Feet" or something the pool store was selling. I was great for about 5yrs. The bottom was smooth and flat and felt spongy under foot. But for the last 2 or 3 yrs, it has all got compressed and is not soft any more and you can see where the seams are. I have 3 places where moles have left tunnels under the bottom so I expect that I might be putting in a new liner next season. I haven't decided what to put down the next time.