The "second skin" comment by Superman was in "It's a Small World After All" (3rd season). It's the episode where Clark/Superman shrinks after using some shampoo made by a high school classmate of Lois.

From the script :
Quote
DR. KLEIN
Your powers are functioning
normally but you've experienced a
significant loss in height and body
mass. I'm not sure why but the
suit fits as snugly as ever.

SUPERMAN
It's the aura effect. Anything
within a tenth of a millimeter is
essentially a second skin.
which implies that Clark knows about his aura.

Also, about the cape. In "Contact", when the microwave transmitter "thingy" is about to explode, Superman uses his cape to protect the others in the room, and they are not "within a tenth of a milimeter" (unless you count that if he touches them, then their whole bodies are).

malu