A cardigan was a item of clothing found in Earth.
Barbara Wright's cardigan was unravelled by Ian Chesterton while they were in the Space Museum so they could ensure they weren't repeating their paths. (TV: "The Dimensions of Time") Barbara later wore another cardigan while on Aridius. It was later used by Ian to set a trap for the Dalek guarding the TARDIS. (TV: "The Death of Time")
St John Colchester often wore cardigans, which he referred to as "cardies". (AUDIO: Escape Room, etc.)