What is the only substance Superman cannot see through?
Lead
Asbestos
Titanium
Vibranium
Back before comics books targeted more serious-minded readers, they were a jumble of made-up, sciencey concepts. Superman’s ability to see through objects with crystal clarity and occasionally melt them with heat vision were both attributed to X-rays, even though that’s not really how they work at all. Real X-rays cannot penetrate lead, however, and writers latched onto that fact to keep Supes from being all-powerful.
Answer: The correct answer is Lead