For the love of all things holy, Sam, stop buying new blue plaid shirts. I’m going to have to just start numbering everything... I swear. Anyway, this shirt is a blue plaid shirt. The light blue stripes are very bright blue against the dark blue of the background. It’s got two breast pockets, on which the plaid runs
Brand: American Eagle
Sam must have run out and bought this in the week and a half he was away from Dean, because the first time we see it is in The Mentalists (7x07). Sam wears it at the end of the episode as he and Dean talk in the cafe and then leave town.
In Bad Boys (9x07), Sam wears this shirt when he and Dean arrive at Sonny’s farm and begin investigating. He keeps it on until after he and Dean torch the bones they believe belong to the ghost, and then changes out of it before he and Dean go to the diner.