The Armadyl Chestplate is a drop from the Kree'arra and the bodyguards. It, along with the Armadyl helmet and Armadyl plateskirt, is part of the Armadyl armour set. The chestplate is statistically superior to every other torso ranged armour other than Morrigan's leather body. Unlike Morrigan's leather body, this armour doesn't degrade, which makes it a more common choice. This is the best nondegradeable Ranged torso armour. The prayer bonus also makes it desirable for the Fight Caves minigame.
Upon the release of RuneScape HD the Armadyl Chestplate was given a slight graphical update. This resulted in a "crop-top" style for male players, exposing the stomach. Needless to say, this change was intended and was not a glitch. The style has since been changed again.
On 8 July 2009, the chestplate had an update (mentioned in Patch Notes 08/07/09) with the release of Mobilising Armies. It seems to be like it was before the HD update, covering the player's stomach on male characters, but exposing the stomach on female characters.