Sam is killing me here with all these different blue plaids. This one has a light counter-colour of either gold or brown that runs through it too. The counter colour roughly falls in four stripes down the vertical front of the shirt, and more along the horizontal. It does up with white snaps.
Brand: Lucky Brand
In Brother’s Keeper (10x23), Sam wears this shirt when he is making bullets in the beginning of the episode, and then when he and Cas go to speak with Rowena. He changes into a suit after he gets the call from Rudy about where Dean is.
In There’s Something About Mary (12x21), Sam is wears this shirt when they get back from the morgue where Eileen’s body was. He wears it until they discover the microphone in the Bunker and lay their trap for the BMoL.
In Wayward Sisters (13x10), Sam wears a plaid shirt very similar to this one at the end of the episode when they say goodbye to Jody. I don’t necessarily think it’s the same one, but it MIGHT be and it’s so similar that I don’t think I need to make a new entry for it.