Atmospheric density jacket

An atmospheric density jacket, or ADJ, was a garment worn to protect the wearer against thin atmospheres. The First Doctor required Ian to don an ADJ when they first began exploring the planet Vortis. He ostensibly produced it from the TARDIS' wardrobe room, without explaining where he had obtained it.

A key feature of an ADJ was the resipiratory compensator affixed to its breast. Ian likened the compensator to an "advanced oxygen mask". (DW: "The Web Planet") The effective life of an ADJ was only about an hour, after which it had to be recharged. (DW: "The Zarbi")