I dunno, depends on the continuity. IIRC Precrisis, kryptonians couldn't break it, or at least had to work very hard to, but Karate Kid did. In 2016, Half Jordan cut through two inches of Inertron and it nearly killed him, and then White Lantern Kyle Rayner cut through a vault two feet thick and it nearly killed him.
I'm also not sure what the upper floor of adamantium actually is. I know of the famous Thor example, but I have heard Gladiator broke it once?
Why is nobody making fun of Half Jordan!? Has this forum gone soft!!?? :P
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