Mizuno Pro 225's are not a cavity back. These are blade irons that offer progressive face thickness to help generate faster club head speeds and offer more forgiveness than traditional blades. , The new Mizuno MP 225 irons are not a cavity back design. They are what is commonly referred to as a blade or muscle back iron which means they are one solid piece with very little forgiveness but an amazing feel. , The Mizuno 225 irons are not cavity back. They are referred to as a "hot metal blade", which means they take the same look as a blade. With the look of a blade, Mizuno designs them to be bigger and thicker to play comparably to some cavity backs.