rubber coated jumper cables

[JointTech]

I was jumping my truck the other day and my buddy let the positive side cable touch the radiator after it was attached to the battery. When I saw it I nearly crapped myself and quick moved it.
He wondered why I was paniced and said most jumper cable jaws are rubber coated so they dont arc.

is that true? I've been walking around like frankenstein for years keeping the red and black away from each other and I spend extra minutes getting the bite good on the posts so it doesnt slip off and arc. now I feel stupid.

These felt like any other painted set I;ve seen but they sure didnt arc when it touched the rad.