Under Armour Heatgear Polo.

It doesn't get much more comfortable than this men's polo. Its extra-stretchy fabric moves with you, not against you. Loose: Fuller cut for complete comfort. In good condition. - Soft anti-pick, anti-pill fabric is extremely breathable & lightweight - 4-way stretch construction moves better in every direction - Anti-odor technology prevents the growth of odor-causing microbes - UPF 30 protects your skin from the sun's harmful rays - 96% Polyester/4% Elastane