Why do my feet get cold in heavy cushion socks when they're supposed to be the warmest?

The most common reason is that the thick socks are making your boots too tight, restricting circulation to your feet. When blood flow is reduced, your feet get cold regardless of how thick the sock is. Other causes include excessive sweating (the thick sock retains moisture that then cools) and cotton-blend construction (cotton retains moisture and provides poor insulation when damp). Try a thinner sock to improve circulation, ensure your socks are merino-based for moisture management, and make sure your boots aren't buckled too tightly.