The foam types are terrible for this purpose. The cheap solution is "musician" type earplugs, which theoretically decrease the total volume while preserving the relative balance of the sound spectrum. I keep pair in my car at all times. I got some at Musician's Friend on the web; I think Guitar Center may carry them in stores. Yes, they attenuate the highs, they do flatten the sound of cymbals a bit too much, but it is better than going deaf.