Moment of Inertia (MOI) refers to the ability to resist rotation (twist). It is on Putter’s Z axis to stay stable and on-line through the downswing (DS) from impact to finish. Typically, Blade putter is around 3000 g/cm2, Mallet is around 4000 g/cm2, Square is around 5000 g/cm2, with some designs like Maximus exceeding 6000 g/cm2.
High MOI design can improve consistency and distance control for off-sweet impact spot with less energy loss and stay online. MOI and "feel" of the putt have an inverse correlation and is compromised based accordance to skill level.