Bone is one of the strongest materials found in nature. It is a rigid connective tissue that has a matrix of collagen fibers embedded in calcium salts. Most of the skeletal system is composed of bone, which provides support for muscle attachment and protects the internal organs. One cubic inch of bone can withstand loads of at least 19,000 pounds (8,626 kilograms), which is approximately the weight of five standard-size pickup trucks. This is roughly four times the strength of concrete. Bone’s resistance to load is equal to that of aluminum and light steel. Ounce for ounce, bone is actually stronger than steel and reinforced concrete since steel bars of comparable size would weigh four or five times as much as bone.