They are mild steel, very light, give loads of power but they are loud as fuck. If you don't care about loud noise they are great (they sound great though) and you really need to give thema coat of paint around the boxes to stop them rusting, and even then they don't lastm that long (2-3 years) but they are pretty good. On a camm'd VTS I didn't notice any performance increase from my BTB when I swapped it for my ashley