Soft robotic actuators used for grasping often have difficulty adjusting their stiffness, which is important for holding objects of different sizes and materials. Twisted string actuators (TSAs) offer a good solution because they can produce strong linear forces and change their stiffness by adjusting the number of twists or the tension in the strings. This study develops a mathematical model to control stiffness in soft robotic fingers using TSAs. By changing the twists in the TSA, the model helps the soft silicone finger adjust its stiffness in real-time while grasping objects. This allows the robot to better handle objects with different properties. Early tests show that this method can improve the robot’s ability to be more flexible and adaptable. This research could lead to better robotic systems that need careful stiffness control, especially for handling delicate objects or working in unpredictable environments.