Exodus 39:21-23

Amplified Bible

²¹ They bound the breastpiece by its rings to the rings of the ephod with a blue cord, so that it would lie on the woven sash of the ephod, and so that the breastpiece would not come loose from the ephod, just as the Lord commanded Moses.

²² Then Bezalel made the robe of the ephod of woven work, all of blue; ²³ there was an opening [for the head] in the middle of the robe, like the opening in a coat of armor, with a hem around it, so that it would not be frayed or torn.