Thermal properties of common materials

What the four properties tell you

Thermal conductivity, k, describes how readily a temperature gradient drives conductive heat flow through a material. Its SI unit is W/(m·K). For the same area, thickness and temperature difference, a high-conductivity layer carries more conductive heat than a low-conductivity layer.

Specific heat capacity, cp, describes the sensible energy required to raise the temperature of one kilogram of material by one kelvin under stated conditions. It is an energy-storage property. It does not tell you how quickly a temperature disturbance moves through an object.

Density, ρ, connects mass and volume. The product ρcp is volumetric heat capacity, which estimates how much sensible energy a unit volume stores for each kelvin of temperature change.

Thermal diffusivity, α, combines transport and storage through α = k/(ρcp). A high value means a temperature disturbance tends to spread through a material relatively quickly. The table calculates diffusivity from the displayed k, cp and density values so the derived result stays consistent with those inputs.

Why copper, water and insulation behave so differently

Copper has very high thermal conductivity compared with common insulation, so it can spread heat effectively through a heat sink, pan base or heat exchanger. Fibrous insulation serves the opposite purpose. Its low effective conductivity helps resist heat flow across a layer.

Water shows why conductivity alone is incomplete. Liquid water does not conduct heat like copper, but its high specific heat lets each kilogram absorb substantial energy for a modest temperature rise. That makes water useful in thermal storage and many heat-transfer systems. In an actual tank or pipe, fluid motion can make convection more important than conduction.

No single thermal property ranks materials from best to worst. A material can be useful because it spreads heat, resists heat flow, stores energy, responds quickly to a changing boundary condition or combines several of those behaviours.

A worked comparison using thermal diffusivity

Thermal diffusivity is calculated as conductivity divided by volumetric heat capacity. Copper combines high conductivity with substantial density, while water combines modest conductivity with high specific heat. Their calculated diffusivities are therefore very different.

This helps explain why temperature changes can spread through a metal object much faster than through a comparable distance of still water when conduction dominates. In liquids, natural or forced convection can move energy much faster than molecular conduction alone, so diffusivity should be interpreted within the actual transport process.

Geometry can matter as much as material choice

Thermal conductivity belongs to a material under stated conditions. Thermal resistance belongs to a particular heat-flow path. For a simple plane layer, resistance increases with thickness and decreases with conductivity and area. A thick layer of a moderately conductive material can therefore resist heat flow more effectively than a very thin layer of a lower-conductivity material.

The same distinction matters in electronics and cookware. A thin copper layer can spread heat laterally while another layer supplies strength. A thermal interface material can conduct far less effectively than the adjoining metal but still improve the complete path by replacing microscopic air gaps and reducing contact resistance.

Temperature, moisture and composition can change the numbers

Thermal properties are condition-dependent. Metal alloy and temper can affect conductivity. Wood varies by species, moisture content and grain direction. Concrete varies with aggregate, density and moisture. Insulation depends on product structure, density, temperature and moisture. Fluid properties vary with temperature, pressure and composition.

That is why every row retains a condition note and source context. Representative values can support education, comparison and preliminary estimates. Product selection, equipment design and safety-critical calculations should use data for the actual material grade or product over the relevant operating range.

Material values are different from assembly ratings

A conductivity value is not an R-value or U-value. R-value describes resistance for a layer or assembly and depends on geometry. U-value describes overall thermal transmittance through an assembly and may include several layers, surface films, framing and other heat-flow paths.

Specific heat also does not determine the thermal mass of an element by itself. The amount of material and its density matter. Comparing complete assemblies therefore requires geometry, boundary conditions and construction details in addition to material-property data.

How to choose a value for a calculation

First match the material as closely as practical: composition, grade, density and physical form matter. Then check whether the reference temperature, moisture level or pressure resembles the intended application. Finally, match the quality of the data to the decision. A representative value may be enough for a sensitivity calculation, while design work may require manufacturer data, a standard, a temperature-dependent correlation or a laboratory measurement.

Do not copy a value without its conditions. Apparent disagreement between reputable references often reflects different temperatures, compositions, test methods or material states rather than a simple error in one table.

How to read the source notes

Some rows use values tabulated directly by an authoritative reference for a stated condition. Others are clearly marked as representative engineering values because a broad material name such as concrete, softwood or fibrous insulation does not identify one unique formulation or product. The condition note tells you which situation applies.

The displayed check date records when the cited context was reviewed for this reference. It does not make a condition-dependent property a universal constant. For precise work, follow the source and confirm that its material definition and test conditions match the problem you are solving.

Use these properties in calculations

Use the Heat Transfer Explorer to see how conductivity affects conduction, the Specific Heat Calculator to connect mass and temperature change to energy, and the Thermal Diffusivity Calculator to combine conductivity, density and specific heat.

For building assemblies, use the Multi-Layer Wall Calculator and read the guides to thermal conductivity, thermal diffusivity and thermal resistance.