A down vest was a down-filled jacket without sleeves, cut off at the shoulders, that was worn in cold weather during the late 20th century.
Jackets filled with goose feather down were first invented by Eddie Bauer, clothing designer for camping and outdoor activities, in 1936. They insulated against the cold so well that his company made flight jackets and other military clothing during World War II. The down vest appeared in the 1960s, and became popular when bronze medal skier Suzy Chaffee, and other skiers, wore brightly colored vests during the 1968 Winter Olympics. 
Marty McFly added a red "Class-5" down vest to his daytime clothes to meet Doc Brown at Twin Pines Mall in the middle of the night, and kept the vest on during the first day he spent in 1955. Passers-by noticed his unusual clothing, and on four separate occasions, someone mistook it for a sailor's life preserver:
- As soon as Marty entered the cafe, Lou, the owner, asked Marty "Did you jump ship?" (an expression referring to a sailor deserting from the navy), since he was apparently still wearing his life preserver.
- While Biff's gang was harassing George, Skinhead jokingly remarked to Biff and the gang, "Get a load of this guy's life preserver. The dork thinks he's gonna drown!".
- As Marty walked downstairs from Lorraine's bedroom, her mother guessed he was a sailor and asked how long he would be in port. Apparently tired of the questions, Marty mentioned the Coast Guard as an alibi.
- When Marty arrived at his house, Doc tried to read his mind. On his third try, he noticed Marty's clothing and guessed he was raising donations for the Coast Guard Youth Auxiliary – amazingly similar to the alibi Marty told Lorraine's mother.
Marty continued to wear the vest until he went to bed at Doc's house that night. After wearing 1950s clothes the rest of the week, he changed back into his 1980s clothes, including his distinctive down vest, after he left the school dance. He wore the vest until he went to bed at his own house in 1985.
- Back to the Future
- Back to the Future novelization
- Back to the Future: The Story
- Back to the Future: The Game