The strongest element known to man inn the Marvel Cinematic Universe was no match for the blade which Thanos was wielding in Avengers: Endgame. Captain America's shield is made of Vibranium, a super strong metal which is mostly found in Wakanda, but Thanos' shield is made of something stronger.
The commentary track attached to the digital downloads of Avengers: Endgame is loaded with intel from the filmmakers. On it, co-directors Joe Russo and Anthony Russo along with screenwriters Stephen McFeely and Christopher Markus open up about each and every plot point through the three-hour journey. Towards the end of the film and its commentary track is where the writers and directors confirmed that Thanos' blade, as was implied by its destruction of Captain America's shield, is stronger than Vibranium.
"You can also see that while Vibranium is the strongest substance on Earth, whatever Thanos' straight razor there is made out of is stronger," Markus said.
"Well, Thanos clearly knew of Eitri," Joe Russo said, which both writers agreed with.
"That's true, he'd have him make him a helicopter blade," McFeely pointed out.
The substance making up the blade Thanos carries in Avengers: Endgame has yet to be identified. Within the Marvel Comics world, there seems to be one element offering up the burden of being the metal in Thanos' blade: Adamantium. Adamantium is an alloy stronger than Vibranium and is not natural but crafted. Adamantium is also more rare the Vibranium according to the Marvel Comics lore.
Then, again, it could be an Uru metal which is an element known only to Nivadellir, the home of Eitri. Eitri also made the Infinity Gauntlet and there has not been an explanation of what metal made Thanos' iconic gold glove bu tit did manufacture Stormbreaker and Mjolnir for Thor.
With the X-Men set to make an eventual debut in the Marvel Cinematic Universe, it's possible the blade from Avengers: Endgame could be studied and broken down, ultimately replacing Wolverine's bones and make him the X-Men character fans know -- with the strongest bones imaginable.
ComicBook.com tried to ask Joe Russo about the metal making up Thanos' blade in Endgame during our Evening With Joe Russo event (seen in the video above) but he was coy with his response and would not commit to Adamantium's existence.
Avengers: Endgame is available now on digital downloads and hits blu-ray on August 13.