An atmospheric density jacket, or ADJ, was a garment which resembled an Earth anorak, worn to protect the wearer against thin atmospheres.

It had been invented by the First Doctor in case an accident on board the TARDIS accidentally deprived him of sufficient air. (PROSE: The Lost Ones)

The suits were, according to the Twelfth Doctor, part atmospheric converter and party comfy suit. (COMIC: The Soul Garden)

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

The Doctor wore an ADJ on his first three visits to Vortis, but not on any subsequent ones. (PROSE: The Lost Ones, The Lair of Zarbi Supremo; TV: The Web Planet) On the third visit, during which Ian also wore an ADJ, the garments ran out of power and were discarded. (TV: The Web Planet)

The Doctor also wore an ADJ while visiting the Ethereal homeworld and Bruhl. (PROSE: The Cloud Exiles, PROSE: Justice of the Glacians)

The Second Doctor, Jamie and Victoria wore atmospheric density jackets while visiting a planet. (PROSE: Valley of Dragons)

The Doctor, Jamie and Zoe wore atmospheric density jackets while visiting Mars. (PROSE: Please Shut the Gate)

The Seventh Doctor, Roz and Chris wore atmospheric density jackets while on Mars. (PROSE: GodEngine)

During a visit to Antarctica in 1915, the Tenth Doctor gave Martha an atmospheric density jacket to keep her warm. (COMIC: The First)

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