I like this one. It’s a dark grey and red plaid. The horizontal stripes stand out more than the vertical. The plaid runs diagonally across the pockets and the shoulder. It does up with buttons, not snaps. It appears to be lined in light grey, as you can see when he rolls up the sleeves.
Sam first wears this shirt in the beginning of Dog Dean Afternoon (9x05), when he and Dean are in the bunker. He wears it again later in the episode when he and Dean are researching at the motel after having visited the vegan bakery.