Thermal conductors are materials that allow heat to pass through them easily. They transfer heat quickly from warmer to cooler parts. Natural examples include metals found in ores deep within the Earth's crust, like copper and iron, which efficiently conduct geothermal heat. Thermal insulators are materials that resist the flow of heat, slowing down its transfer. They prevent heat from moving easily. Natural examples include air trapped within animal fur or bird feathers, which acts as an excellent insulator to keep animals warm, and dry soil, which insulates underground burrows from temperature extremes.