A modular insole for an article of footwear is disclosed. The modular insole comprises a shell portion having a first surface arranged to face a foot of a wearer of the article of footwear and a second surface arranged to face away from the foot of the wearer; and a stiffening element capable of being removably coupled to the second surface of the shell portion and arranged to modify a stiffness of the modular insole when the stiffening element is coupled to the shell portion. A method and a machine-readable medium are also disclosed.