Maybe it’s just me, but this colour brown always makes me think of the 70s. This plaid shirt has buttons and only one breast pocket on the left (which is hard to see). It’s a very gradual medium plaid.
It first appears in Hunted (2x10), when Sam wears it on his second day in Lafayette, Indiana. He wears it to break into the psychiatrists office and keeps it on for the rest of the episode.
In Tall Tales (2x15), Sam is wearing this shirt in the flashbacks of him and Dean investigating the Professors death. He changes before they interview the jock about the abduction though.
In All hell Breaks Loose Part 2 (2x22), Sam is wearing it when he and Dean arrive at Bobby’s house. He keeps it on for the rest of the episode.
In Sex and Violence (4x14), Sam is wearing it when he returns to the hotel room to find Dean infected with Siren venom.
In The Curious Case of Dean Winchester (5x07), Sam is wearing it at the end of the episode when he leaves to get his booster shot.
In Abandon All Hope (5x10), this is the shirt that Sam wears to Carthage to try to kill Lucifer.
In Point of No Return (5x18), Sam wears this shirt for the entire episode.
In You Can’t Handle the Truth (6x06), Sam wears this shirt at the very beginning of the episode when he and Dean are in the park, and Sam finds the case in the paper.
In Defending Your Life (7x04), Sam wears this shirt once he changes out of his suit from the beginning of the episode. He keeps it on until he has to put back on a suit to go investigate the second murder of the episode (the guy who was killed by a ghost dog).
In There Will Be Blood (7x22), Sam wears this shirt for the entire episode.
In Survival of the Fittest (7x23), Sam continues to wear this shirt for the entire episode.
In Man’s Best Friend With Benefits (8x15), Sam wears this shirt at the beginning of the episode when he and Dean arrive and Portia shows up to explain the situation.
In Heaven Can’t Wait (9x06), Sam is wearing this shirt when Dean calls back to the bunker to check in, once he gets to Idaho. At this point, Sam and Kevin have struck a dead end with their own research and Dean suggests asking Crowley – Sam wears the shirt until the end of the episode.
In Captives (9x14), Sam wears this shirt when he and Dean are preparing to deal with the ghost that appears to be haunting the Bunker. He wears it up until he and Dean put on suits to investigate the storage facilities.
In The Things We Left Behind (10x09), Sam wears this shirt when he and Dean meet up with Cas. He takes it off briefly to change into a suit while speaking with the social worker, but then changes back into it when he meets back up with Cas and Dean.
In Our Little World (11x05), Sam wears this shirt at the end of the episode when he and Dean talk to Cas in the Bunker.
In Don’t You Forget About Me (11x12), Sam wears this shirt from the beginning of the episode, and is still wearing it when they get to Jody’s and have dinner with her and the girls.
In The Chitters (11x19), Sam wears this shirt when he and Dean are in the bunker at the beginning of the episode.
In Exodus (13x22), Sam continues to wear this shirt until after he and Dean are finally able to have their reunion hug when alone. He then changes into some borrowed clothes.
FATE: In Beat the Devil (13x21), Sam is killed by vampires while wearing this shirt (and subsequently resurrected by Lucifer). It gets half the collar torn off and severely bloodstained: