Heat conduction, also called thermal conduction, is the transfer of thermal energy through a material or between materials in direct contact because of a temperature difference. In conduction, energy moves from the hotter region to the colder region without bulk motion of the substance as a whole. Everyday examples include a metal spoon warming in a hot cup of tea, a hand warming on a hot-water bottle, or heat leaking out of an uninsulated home.

How conduction works

On a macroscopic level, the rate of conductive heat transfer depends on three basic factors: the temperature difference, the area through which heat flows, and the thickness or path length between hot and cold zones. These relationships are summarized by Fourier's law of heat conduction, which states that heat flux is proportional to the negative of the temperature gradient and to a material property called thermal conductivity. Thermal conductivity characterizes how well a material conducts heat; it varies widely between metals, ceramics, polymers and gases.

Microscopic mechanisms and material differences

Different materials conduct heat by different microscopic carriers. In metals, free electrons carry a large fraction of thermal energy; in nonmetallic solids, lattice vibrations (phonons) are the dominant carriers. In gases and liquids, collisions between molecules transmit energy, but because particles are more widely spaced, conduction is generally much weaker than in solids. Materials engineered to have low thermal conductivity are used as insulators; those with high conductivity are chosen for heat sinks, cookware, and thermal interfaces.

History and formulation

The mathematical description of conduction was developed in the early 19th century, most notably by Joseph Fourier, whose work introduced the differential relation now known as Fourier's law. That work brought conduction into the broader framework of heat transfer and thermodynamics and enabled quantitative design in engineering and science. Since then, analysis has been extended to transient (time-dependent) conduction, anisotropic materials, and nanoscale regimes where classical descriptions must be refined.

Applications and examples

  • Building insulation and thermal barriers to reduce unwanted heat loss or gain.
  • Cookware and stovetops designed to conduct heat rapidly and uniformly.
  • Electronic cooling: heat sinks, thermal interface materials and spreaders rely on conduction to move heat away from components.
  • Geology and planetary science: conductive heat flow helps determine temperature profiles in the Earth and other bodies.

Relation to other heat transfer modes

Conduction often occurs together with convection and radiation. Conduction transfers energy through solids or between touching surfaces; convection involves bulk fluid motion that carries heat, and thermal radiation transfers energy by electromagnetic waves without a material medium. At an interface, contact resistance and imperfect surfaces can reduce the conductive heat flow. Engineers commonly combine these modes in models to predict real-world heat exchange.

Further reading and practical guidance

Practical assessment uses the concept of thermal resistance, layered material models, and measured values of thermal conductivity. For experimental methods and advanced treatments, see introductory texts and resources that present Fourier's law, transient conduction solutions, and microscale transport theory. For a concise overview of what conduction means in everyday phenomena, consult an accessible primer or glossary entry on heat transfer.