Pro-Mesh Combo Umpire Cap by Richardson.  Heavyweight, two layer, ProMesh fabric.

Mesh Umpire Cap Features

• 2 layer pro mesh fabric
• Matching colored undervisor and black sweatband  
• ProCrown shape with ProBuckram fused to front panels
• Matching color undervisor and black sweatband
• 1 3/8 ProSweatband with twill face and nylon backing
• Pre-curved PE visor with four rows of stitching, 2 inch length
• Fitted sizes: 6 3/4 - 8
• Available in Navy and Black

Navy vs. Black
Navy umpire caps are generally a dark navy, so dark they look black until you actually compare them to to a black cap. Navy is the most popular color. You won't go wrong with the navy unless your umpire association requires a black cap.