You temporarily transport the armor used as the material component, placing it on the boundary between the Ethereal Plane and your current plane of existence (the spell fails and the casting is wasted if you are already on the Ethereal Plane). The armor disappears into the Ethereal Plane. As a bonus action while the armor is in the Ethereal Plane and you are not wearing a different set of armor, you can instantly summon and don the armor. If the armor is taken off of you by any means, or if you choose it to as a bonus action, the armor returns to the Ethereal Plane. If the armor is on the Ethereal Plane when the spell ends then it is instantly summoned to your current plane of existence and donned by you, or it appears in a space within 5 feet of you if you are already wearing armor.