Uniqlo Heattech Undershirt

Uniqlo's Heattech undershirt is thin enough to wear under a button-down without adding bulk. The fabric generates warmth from body moisture using a fiber technology that the company developed with Toray Industries. It costs $15, comes in 3 weights for different climates, and the fit is slim without being tight. That it doesn't look or feel like a technical garment, which is the whole point because an undershirt that announces its own cleverness defeats the purpose. The crew neck sits low enough that it does not show under an open collar, and the seams are flat-locked so they don't create ridges under a fitted shirt. Fifteen dollars for a technical base layer is the kind of pricing that just makes you buy two.