Not the ephod itself, for that was prescribed before, Exodus 28:6, but a long and loose robe called the robe of the ephod, because it was worn next under it, and was girded about the high priest's body with the curious girdle of the ephod.
Related Commentaries of Exodus 28:31
Exodus 28:31
31 And thou shalt make the robe of the ephod all of blue.