The moment of inertia is a propertie of the section, as the perimeter or the area, do not depend of the type of material.
It reflect the concentration of material away of the center of gravity. The circunference (not the circle)is the perfect section because has the most of his material away of the center, while the circle is the worst section.The stress in any section due to moment, torsion and axial load with eccentricity are reduced when the inertia are increased. Thats is the reason why it's is a very important section property for design. Sorry if my answer don't was enough.
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