EI Profile

An EI profile describes how stiff a golf shaft is at different points along its length.

“E” stands for modulus of elasticity and “I” refers to the moment of inertia. Together, they show how much each section of the shaft resists bending.

Manufacturers measure stiffness from the butt to the tip, creating a curve that shows where the shaft is firm, where it’s softer, and how smoothly those sections transition.

Fitters use EI profiles to understand how a shaft will feel and perform for different swing types. Two shafts labeled the same flex can behave very differently if their EI profiles are shaped differently.

A shaft with a stiff midsection and softer tip will launch higher with more spin. One with a firm tip and softer butt may feel smoother but produce a lower, more controlled flight.

Matching the EI profile to the golfer’s tempo, transition, and release helps create a predictable ball flight and a shaft that feels natural in the player’s hands.