'Breastplates' in the Bible

They had breastplates, like breastplates of iron. The sound of their wings was like the sound of chariots, or of many horses rushing to war.

Thus I saw the horses in the vision, and those who sat on them, having breastplates of fiery red, hyacinth blue, and sulfur yellow; and the heads of lions. Out of their mouths proceed fire, smoke, and sulfur.