'Breastplates' in the Bible

They had breastplates like breastplates of iron; and the sound of their wings was like the sound of chariots, of many horses rushing to battle.

And this is how I saw in the vision the horses and those who sat on them: the riders had breastplates the color of fire and of hyacinth and of brimstone; and the heads of the horses are like the heads of lions; and out of their mouths proceed fire and smoke and brimstone.