The shirt jac is the one a lot of carriers wear as their outer layer on cooler mornings — it's cut heavier and more structured than a standard shirt, sits open like a light jacket over a long sleeve or a t-shirt, and still looks uniform-correct on the route. If you've been alternating between shirts and jackets depending on the morning temperature, this is the piece that covers both.
 
Double ply straight yoke means the back holds its shape after washing. Convertible collar with internal stays so it looks sharp worn open or buttoned. Tagless neck so there's nothing rubbing at the collar all shift.
 
Construction details:
 
• 65% polyester / 35% cotton poplin, 4.2 oz
• Top-fused convertible collar, internal stays
• Double-ply straight yoke for structure and durability
• Short sleeve cut — pair over a long sleeve on shoulder-season mornings
• Tagless collar label
• Machine wash warm, tumble dry
• Regulation USPS postal blue
Fit: Runs a touch roomier than the standard shirt to allow layering. If you're wearing it buttoned as a standalone shirt, you may want to size down one. If you're planning to layer a long sleeve underneath, your normal size works.
 
USPS compliant. Uniform allowance eligible.