In infrared thermography, which combination of emissivity and reflectivity does aluminum typically exhibit?

• A. Low emissivity and high reflectivity
• B. High emissivity and low reflectivity
• C. Moderate emissivity and moderate reflectivity
• D. High emissivity and high reflectivity

Answer: (A)

Polished aluminum tends to act like a good infrared mirror rather than a strong emitter. Emissivity measures how much infrared energy a surface emits compared with a perfect emitter, while reflectivity measures how much infrared energy from the surroundings is reflected by the surface. For aluminum, especially when its surface is smooth, the emissivity is low, meaning it doesn’t radiate away much IR on its own. At the same time, its reflectivity is high, so it reflects a large portion of the infrared coming from the surroundings. In the common infrared range used by thermography, polished aluminum can have emissivity around 0.05–0.1 and reflectivity well over 0.8.

This combination explains why a thermal camera can show the temperature of nearby objects reflected off the aluminum surface, rather than the aluminum’s true temperature, unless you compensate by setting a correct emissivity value or applying a nonreflective coating to raise emissivity. So the best match is low emissivity and high reflectivity.