What's Up With Captain America's Shield?

Back when "Captain America: The Winter Soldier" came out, our BrainStuff team got super excited. We even drew cartoons of ourselves as the Avengers.

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BrainStuff host and Stuff You Should Know podcaster Josh Clark does the honors as Captain America.
Christian Sager

We also investigated how Captain America's shield might work, and the above video was the result. Now if you go see "Captain America: Civil War," you'll be fully in the know. Here's the scoop.

The official Marvel database says that Captain America's shield is a metal disc that's approximately 2.5 feet (0.76 meters) in diameter and weighs 12 pounds (more than 5 kilograms). But Rhett Allain at Wired did some math and figured out that it would more likely weigh 43.9 pounds (19.9 kilograms). The super shield is made of a unique alloy combining vibranium (a fictional metal), steel and an unknown third component.

In the "Captain America" comics, the story goes that Dr. Myron MacLain was attempting to replicate Hercules' golden mace by fusing vibranium with an experimental iron alloy. Some say it was a steel alloy, but even MacLain didn't know what it was ... because he fell asleep when an unknown catalyst was introduced to the process. He was never able to duplicate what he did, so the government painted the disc and gave it to Captain America. Of course.

How would you forge such a thing, especially since metallurgy is so complicated? Remember that forgeability is how easy or difficult a material resists deformation. Since Captain America's shield is indestructible, it would have a very narrow forging temperature range, meaning it could only be forged for a short time after heating. With metallurgical factors like crystal structure, chemical composition and grain size at play, the only way MacLain could have diminished their influence would be by adding alloying elements, possibly compounds that easily dissolve within the metal.

All types of elements could have been introduced. But, it's likely that Captain America's shield was forged like a superalloy. This is how metallurgists refer to iron-, nickel- and cobalt-based alloys, specifically the ones that offer very high strength at high temperatures. Of these high-strength metals, iron-based grades are the least difficult ones to work with. So that would narrow down MacLain's experimental alloy to iron.

And how do we explain the shield's ability to absorb kinetic energy, supposedly from the vibranium in the alloy? Usually materials absorb kinetic energy through other mechanisms, like plastic or elastic deformation, or dynamic fluid flow. But Cap's shield doesn't seem to be an elastomeric material, and it's not organic like polyurethane.

In the movies it actually seems to reflect vibration, rather than absorb it. Like when Thor hits it with Mjolnir in the first "Avengers" movie and the shock wave flattens a whole forest. Perhaps that was because the shield reached its absorption limit?

Another thing that's tough to explain is how aerodynamic the shield is. If it really weighed 43.9 pounds, it would be difficult to throw, even for a guy in peak physical condition like Steve Rogers. In the comics, Tony Stark actually puts electromagnets under the shield to help control it mid-flight. But Captain America later ditched them because they upset the shield's natural balance.

Seems like the soldier and the shield are made for each other.