An integral part in the field of soft robotics is the ability to tune material stiffness. This adaptability is inspired from the natural ability of organisms to alter their stiffness to perform various tasks. The most common approach to mimic this ability is through granular jamming, where a granular material switches between fluid and solid-like states based on density alterations caused by vacuum pressure. In this thesis, a cuboid composite material is introduced, containing internal cylindrical chambers arranged in distinct matrix configurations (2x2, 3x3, and 4x4). A custom-designed pneumatic system enables precise control over this transition, allowing for selective modulation of stiffness across different regions of the material by applying differing pressures to specific regions of the composite material. This approach not only allows for rapid changes in stiffness, but enables stiffness to be adjusted uniformly throughout the material or localized to specific areas. This approach also allows for predictive modeling of granular composites to better understand its mechanical response under differential pressures. / Master of Science / Soft robotics is a field that mimics the flexibility of living organisms such as octopi, geckos, etc., to create machines that can adapt to various tasks and environments. One of the unique features of these robots is their ability to change how stiff or soft they are, much like an octopus can alter the rigidity of its tentacles when gripping an object. A method called granular jamming is at the heart of this technology. It involves using materials made up of tiny particles, like coffee grounds or sand, that can switch between flowing freely like a liquid and locking together like a solid. This switch is controlled by changing the space between the particles, usually by sucking out air to pack them tightly. The research in this thesis introduces a special type of material designed as a rubber-like cube containing multiple small cylindrical compartments arranged in different patterns, such as 2x2 or 4x4 grids. Each compartment is filled with these unique particle-based materials, in this particular instance, the material is coffee grounds. We use a specially designed air pressure system to selectively adjust the air pressure in these compartments, making the material stiffer or softer as needed. This allows us to control the stiffness with great precision, either uniformly across the whole block or in specific areas. The experiments conducted in this thesis show a clear pattern: the more air pressure is decreased (making it more negative), the stiffer the material becomes. This finding confirms that granular jamming is a promising strategy for rapidly and precisely controlling material stiffness for future soft robotic applications.