system
Given the following post, respond as if you're commenting on Reddit:
human
I want to create Captain America's shield. What is the overall toughest stuff we can make these days?
gpt
No material strength will prevent conservation of momentum for ruining your day when you get hit by a 75+ mm tank shell.  Conservation of momentum guarantees that you'll be destroyed.  

Anyway, the best armor material varies greatly by projectile.