"What is the arenak armour they're wearing?" "Arenak is a synethetic metal, almost perfectly transparent. It has practically the same refractive index as air, therefore, it is, to all intents and purposes, invisible. It's about 500 times as strong as chrome-vanadium steel, and even when you've got it to the yield point it doesn't break, but stretches out and snaps back, like rubber with the strength unimpaired."

1968