Captain America's only weapon is his shield, a concave disk 2.5 feet in diameter, weighing 12 pounds. It is made of a unique Vibranium-metal alloy that has never been duplicated. The Shield was cast by American metallurgist Dr. Myron MacLain, who was contracted by the U.S. government to create an impenetrable substance to use for tanks during World War II. During his experiments, MacLain combined Vibranium with an unknown steel alloy he was working with and created the disc-shaped shield. MacLain was never able to duplicate the process due to his inability identify a still unknown factor that played a role in it. The shield was awarded to Captain America by the government several months after the beginning of his career.
The shield has great aerodynamic properties: it is able to slice through the air with minimal wind resistance and deflection of path. Its great overall resilience, combined with its natural concentric stiffness, enables it to rebound from objects with minimal loss of angular momentum. It is virtually indestructible: it is resistant to penetration, temperature extremes, and the entire electromagnetic spectrum of radiation. The only way it can be damaged in any way is by tampering with its molecular bonding.