Modulus

Modulus
The measure of a fiber's stiffness or resistance to bending. The higher the modulus, the stiffer the material.
Moisture Cure Polyurethane ...

MODULUS - A measure of stiffness. It refers to a material's ability to resist
bending or stretching. The higher the modulus, the stiffer the fiber.

A High-Modulus graphite shaft is somewhat stiffer.
Also there are Bi-Matrix club shafts, they are made of graphite and steel. Bi-Matrix woods have a graphite shaft with a steel tip. Bi-Matrix irons have a steel shaft and a graphite tip.

See also: Shaft, Hosel, Metal, Hit, Iron