After much research by the Bloon Empire, steel has been found to be MUCH tougher than lead! Guess what they decided to do with this advantage... If you guessed "new bloons made of steel", you're correct. Also, there are three different types of steel bloon, being the Stainless Steel Bloon, the Carbon Steel Bloon, and the Low-Background Steel Bloon. Oh, and did we mention that they are IMMUNE TO ALL THINGS THAT LEADS ARE IMMUNE TO? Oh, and speaking of which, all three types contain a single lead bloon.