Thermal conduction

Assume that the temperature of the inside of your foot is always the same and the temperature 'below the floorboards' is also the same. There will be a thermal gradient from your body tissue, across your skin, through any insulation and the floor. If the intermediate layer has low conductivity, the surface of your skin will have a higher temperature (It's not just an illusion) because there will be a greater temperature drop across the insulation layer and the overall rate of heat flow will be lower.

There is a direct analogue here with an electrical potential divider, consisting of a chain of resistors, where the PD is shared across the resistors. Inserting a high value of resistor in series with a resistor will reduce the total current, which will reduce the PD across the original resistor.