Conduction
Heat transfer through direct contact between two materials — the mechanism behind cast iron searing.
Conduction is the transfer of thermal energy from one material to another through direct physical contact. When a steak sits on a hot cast iron skillet, heat flows from the metal surface into the meat at the point of contact. No air, no water, no radiation involved — just molecule-to-molecule energy transfer.
The rate of conductive heat transfer is governed by Fourier's law: the heat flux is proportional to the temperature difference between the two surfaces and the thermal conductivity of the materials. Cast iron has a thermal conductivity of about 52 W/m·K, which is moderate among metals but combined with its substantial thermal mass, makes it excellent for sustained high-heat searing.
Why conduction matters for steak: When you sear in a pan, conduction is the dominant heat transfer mechanism. A flat cast iron surface provides nearly 100% contact with the steak's bottom face — every point is touching hot metal. This is why cast iron produces more uniform browning than grill grates, where contact occurs only on the narrow grate lines.
Practical tip: For maximum conduction efficiency, press the steak flat against the pan. Any air gap — from a curved surface, uneven cut, or warped pan — interrupts conductive contact and creates uneven browning.