Emissivity of Common Surfaces
Total emissivity of 18 common surfaces, with reflectivity and the radiation emitted at 100 C.
A hot surface loses heat by thermal radiation, and how much depends on its emissivity (ε), from 0 for a perfect reflector to 1 for a perfect black body. Polished metal has a very low emissivity, and paint, glass, brick and skin have a high one. This is why a bare shiny pipe loses little heat by radiation and a thermos flask is silvered.
The table lists typical total emissivity for 18 surfaces near room temperature, the matching reflectivity of an opaque surface and the radiation emitted at 100 C.
The table
| Surface | Total emissivity (near room temperature) | Reflectivity of an opaque surface (1 - emissivity) | Radiation emitted at 100 C (W/m2) |
|---|---|---|---|
| Aluminum, polished | 0.05 | 0.95 | 55 |
| Aluminum, commercial sheet | 0.09 | 0.91 | 98.9 |
| Aluminum, anodized | 0.77 | 0.23 | 846.5 |
| Copper, polished | 0.03 | 0.97 | 33 |
| Copper, oxidized | 0.65 | 0.35 | 714.6 |
| Steel, polished | 0.07 | 0.93 | 77 |
| Steel, oxidized | 0.79 | 0.21 | 868.5 |
| Stainless steel, polished | 0.075 | 0.925 | 82.5 |
| Cast iron, oxidized | 0.64 | 0.36 | 703.6 |
| Paint, black matte | 0.95 | 0.05 | 1044.4 |
| Paint, white | 0.9 | 0.1 | 989.4 |
| Glass | 0.92 | 0.08 | 1011.4 |
| Brick | 0.93 | 0.07 | 1022.4 |
| Concrete | 0.94 | 0.06 | 1033.4 |
| Wood | 0.9 | 0.1 | 989.4 |
| Water | 0.96 | 0.04 | 1055.4 |
| Human skin | 0.97 | 0.03 | 1066.4 |
| Asphalt | 0.93 | 0.07 | 1022.4 |
Source and notes: Typical total hemispherical emissivity near room temperature (Cengel and Ghajar, Heat and Mass Transfer, Table A-18; ASHRAE Handbook, Fundamentals). Emissivity depends strongly on finish, oxidation and temperature, so a polished metal can read many times lower than the same metal oxidized. Radiation emitted = emissivity x 5.670374419E-8 x T^4 (T = 373.15 K), without the surroundings.
How to use this table
- Find the surface and its finish (polished, oxidized, painted).
- Radiated power per area = ε σ T⁴ with σ = 5.67 × 10⁻⁸ W/m²·K⁴ and T in kelvin.
- For net exchange with surroundings at Ts use ε σ (T⁴ − Ts⁴).
- Set the emissivity on an infrared thermometer or camera to the surface you are measuring.
Worked example: a 100 C surface in a 20 C room
- Net radiation = ε σ (373.15⁴ − 293.15⁴) = ε × 681 W/m².
- Polished aluminum (ε = 0.05): 34 W/m².
- Black matte paint (ε = 0.95): 647 W/m², 19 times more. Painting a hot part black makes it cool faster; leaving it shiny keeps it warm.
Notes and cautions
- Emissivity depends strongly on the finish, oxidation, temperature and wavelength. The table gives a typical room-temperature value.
- An infrared thermometer set to 0.95 reads a shiny metal surface far too low: put tape or matte paint on the spot, or look up the emissivity.
- For a body in a room, convection often removes more heat than radiation does; radiation dominates at high temperature and in a vacuum.
Related tools and guides
- Heat Transfer (guide)
- Thermal Conductivity of Materials
- Heat Sink and Thermal Resistance Calculator
- All reference tables
FAQ
What is the emissivity of polished aluminum?
About 0.05; anodized aluminum is about 0.77, which is why black anodized heat sinks radiate well.
What emissivity for an infrared camera on skin?
About 0.97 to 0.98.
Sources
- Cengel and Ghajar, Heat and Mass Transfer, Table A-18; ASHRAE Handbook, Fundamentals; the Stefan-Boltzmann constant from CODATA 2018.
- Typical total hemispherical emissivity near room temperature (Cengel and Ghajar, Heat and Mass Transfer, Table A-18; ASHRAE Handbook, Fundamentals). Emissivity depends strongly on finish, oxidation and temperature, so a polished metal can read many times lower than the same metal oxidized. Radiation emitted = emissivity x 5.670374419E-8 x T^4 (T = 373.15 K), without the surroundings.