A guy over at Harmonic Discord had access to the equipment to test the mechanical and acoustic properties of different foams. He found that one of the best bass traps you can buy is to get a roll of rebond foam carpet pad and stand it in the corner. A roll measures about 18"x6' and costs about $60. You could cover it with fabric to give it a tube sub look. I thought that was a really cool way to save a whole bunch of money over the commercial products. You could probably even return it to the carpet store and get your money back if it didn't work for you. Hmmm, HD seems to be down. I'll post a link when it's back up. Okay here's the link.