An incredibly hot one-piece bat, B21-Hot Metal combines Mizuno's powerful Hot Metal single wall aluminum alloy with innovative CorTech technology, which adjusts wall thickness across the barrel to create a high-performance bat with an aggressive sweet spot. Engineered details like ...An incredibly hot one-piece bat, B21-Hot Metal combines Mizuno's powerful Hot Metal single wall aluminum alloy with innovative CorTech technology, which adjusts wall thickness across the barrel to create a high-performance bat with an aggressive sweet spot. Engineered details like an optimized end cap create a booming sound, while also increasing the size of the sweet spot to give you the ultimate one piece bat.