The classic 50/50 knit polo. This is the shirt most carriers end up living in — soft enough off the shelf that you don't need to break it in, heavy enough at 5.3 oz to hide an undershirt and not turn translucent after a rain shower.
 
Top-fused convertible collar so you can wear it buttoned clean or popped open without the collar curling. Long back tail that stays tucked through a full shift, and a tagless neck so nothing rubs raw on a hot day.
 
The details:
 
• 50% polyester / 50% cotton piqué knit, 5.3 oz
• Top-fused convertible collar, internal stays
• Left chest pocket, embroidered USPS eagle
• Extended back tail — stays tucked all shift
• Tagless neck label
• Plain hemmed sleeves, regulation USPS light blue
Fit: True to size. The 50/50 shrinks a little on the first wash — maybe a half size through the chest. If you want a relaxed fit or plan to layer, size up once.
 
Machine washable. USPS compliant. Uniform allowance eligible.