The material that Thanos sword is made of remains undefined and is a topic of debate among fans. However, there are some theories and confirmed facts that provide a starting point. According to the commentary track on the Endgame Blu-Ray, Thanos sword comes from somewhere off-world, making it stronger than vibranium. Thanos uses it to sheer off the top of Captain Americas supposedly "unbreakable" shield in Endgame, which is a big part of why the weapon remains such a hotly debated topic. Some theories suggest that the sword could be made of Uru, a metal that is stronger than vibranium and is used to make Thors hammer. Other theories suggest that it could be made of adamantium, a metal that is known for its indestructibility and is used in the X-Men franchise. However, adamantium is a man-made mineral, which wouldnt explain the swords presence in Thanos hands. Another theory suggests that it could be made of Plandanium, a metal that the Space Knights of Galador use to make their armor. In conclusion, the material that Thanos sword is made of remains a mystery, but it is clear that it is one of the most powerful weapons in the Marvel Cinematic Universe.