Well, also in 'Don't Tug On Superman's Cape,' when the tiny helicopter that targets Clark at his apartment destroys most of his Suits, Lois says that she thought they were invulnerable, and Clark replies that he has an aura that extends from his skin to protect them when he's wearing them.
Don't know if that helps or not...
ETA: Just read more carefully (as I should always try to do
) and saw that you want Klein and Superman. Sorry. I'll just tiptoe out now.