I built a seat over the summer. I went to arco upolstry, they are a boat seat shop. they build custom boat interiors. I bought foam from them. It cost me $24 for 2 pieces that were like 24 inches long by 16 inches wide and 4 inches thick. I then glued those together for a piece that was 8 inches thick. Then took the turkey carving knife to it. At the time I built it I thought that foam I bought was firm enough, now I realize it isnt. Make sure you get foam that is STIFF. The seat I built was about 3,5 inches taller then stock and like 5 pounds lighter.