Source: Knights of the Inner Sea, pg(s). 30
The Armiger's panoply is actually a set of items—two bracers and a sack. The sack can hold only a single suit of armor, including a shield. If anything else is put into the sack, it falls right through. The bracers are masterwork forearm guards common to padded or quilted armor. When the bracers' wearer speaks a command word, the armor and shield in the sack are teleported onto the wearer, swapping armor if necessary.