High Emissivity Materials, Labels, and Paints for Reliable Thermal Inspections

High Emissivity Materials: In This Article

Let’s look at how high emissivity materials affect thermal imaging, which surfaces naturally emit radiation well, and when labels, tape, paint, or another coating may be useful. Later sections compare these choices and cover common errors around polished metals and reflective surfaces.

Bare metal connections are common targets during electrical inspections. They are also some of the hardest surfaces to measure with a thermal camera.

Take a shiny metal busbar. It has low emissivity, so it behaves less like a measurement surface and more like a mirror. Some of the infrared energy on the screen may be reflected radiation from the room, not energy emitted by the actual target surface. The displayed temperature can therefore be misleading.

Mark the inspection point with a high emissivity label, electrical tape, or a patch of paint. The camera then has a known surface to measure.

The idea is simple: prepare a small surface with known emissivity and record where it is. This is the target you’ll use in future inspections. This makes temperature measurements easier to compare without changing the equipment being monitored.

What Are High Emissivity Materials?

Emissivity describes an object’s ability to emit thermal radiation from its surface. It is stated as a ratio from 0 to 1.

An ideal black body has an emissivity of 1. This theoretical black body absorbs all incident radiation and acts as a perfect emitter at a given temperature. Under Kirchhoff’s Law of Thermal Radiation, good absorbers of radiation are also good emitters. The terms perfect blackbody, perfect black body, and blackbody all refer to this same reference model.

Actual materials fall below 1. High emissivity materials are surfaces that emit a large fraction of their thermal energy as infrared radiation, typically with emissivity values near 0.90 or higher. Common examples include matte paint, rubber, plastics, ceramics, oxidized metals, and purpose-made labels or tape used to improve thermal imaging accuracy.

Two objects can sit at identical temperatures and look completely different on a thermal image. A material’s emissivity defines the object’s ability to produce a trustworthy infrared reading, which is why this matters to maintenance managers, reliability engineers, electrical engineers, plant managers, operations directors, safety professionals, and asset management teams responsible for safe, accurate inspections. Matte paint holds a stable reading. Polished metal next to it picks up whatever the room is throwing at it, be it a nearby motor, a pipe, or the person holding the camera. What shows up as a temperature difference on the image may not be a temperature difference at all.

Bad readings can affect predictive maintenance decisions. They can also lower the reliability of the inspection. High emissivity surfaces are generally easier to measure with thermal imaging. Polished metals and other reflective surfaces are more likely to cause errors. Labels, tape, or paint can improve measurement accuracy on those targets, reduce false readings, and help prevent unplanned downtime.

Radiative heat transfer is governed by the Stefan-Boltzmann law:

M = εσT⁴

In this relationship, M represents radiant exitance (emitted power per unit area in W/m²), ε is surface emissivity, σ is the Stefan-Boltzmann constant, and T is absolute temperature in Kelvin (K). At elevated temperatures, radiant energy output increases exponentially due to the fourth-power temperature relationship.

A thermal camera works over a limited wavelength band, however. Spectral emissivity can change at different wavelengths. Material emissivity also changes with surface finish, oxidation, corrosion, coatings, and temperature. For that reason, a handbook value should be treated as a starting point rather than a permanent setting.

Why High Emissivity Matters in Thermal Imaging Inspections

An IR camera picks up more than just what the target is putting out. Surface emissions, background heat bouncing off the target, energy transmitting through thin materials — it all hits the array together. Miss the reflected ambient compensation on a reflective surface and the temperature calculation falls apart before it even gets started.

High emissivity improves the share that comes directly from the object surface. The camera has less reflected radiation to sort out, so the temperature measurement is generally more stable.

Low-emissivity metals create the opposite problem. Polished aluminum, with an emissivity of 0.03 to 0.05, plus copper and stainless steel, behave much like thermal mirrors. A technician, a hot motor, or sunlight entering the area may appear as a warm reflection. Change the camera angle, and the apparent hot spot may move.

This can affect more than one reading. If inspections are performed from different positions each time, reflected energy can make a healthy connection look inconsistent from one route to the next.

A known high emissivity target reduces that uncertainty. For example, a label or approved tape placed on a de-energized connection can provide a repeatable surface for future thermal imaging. The camera’s emissivity setting is matched to the target rather than estimated from the shiny metal underneath.

The target must have time to reach the same temperature as the component. Its size must also cover the camera’s measurement area at the inspection distance. A label that appears visible on the screen may still be too small for an accurate measurement.

However, a high-emissivity target isn’t enough to solve the entire measurement problem. Calibration, focus, distance, equipment load, reflected apparent temperature, and infrared window transmission can still change the reading.

Prepare these reference points while the electrical equipment is open and de-energized. This is especially useful when the target will later be inspected through an infrared window. IRISS: Emissivity in Thermal Imaging. IRISS: Emissivity in Thermal Imaging

Common High Emissivity Materials and Their Emissivity Values Used in Industry

Many common materials in industry emit heat more effectively than bare polished metals. Painted surfaces, rubber, plastics, ceramics, and some forms of insulation commonly fall in the high-emissivity range. Different materials can also show different emissivity values depending on surface finish, oxidation, and overall condition.

Oxidation can also change a metal surface. Clean copper has low emissivity, but oxidized copper emits more infrared radiation. Rust and corrosion can produce a similar change on iron or steel. The exact value depends on how much of the surface is covered and whether the condition is uniform.

These emissivity values are determined from published data, test conditions, or manufacturer references. Before using one, check the target’s condition and the camera manufacturer’s data. A coating that is damaged, dirty, exposed to oil, or partly missing may no longer provide a uniform measurement surface.

FLIR reports that many flat paints fall near 0.90 to 0.95 and that good-quality black electrical tape is commonly around 0.95. It also cautions that tape must be opaque within the camera’s wavelength range. (FLIR: Using Materials to Increase Target Emissivity)​

High Emissivity Labels and Tape for Reliable Measurements

Labels and tape work well when an inspection needs a defined measurement point. Instead of estimating the emissivity of shiny metal, the technician measures the object through a small surface with a known emissivity value.

A common choice is Black electrical tape, and many of them have an emissivity near 0.95. Kapton tape is also used in some measurement setups and has an emissivity of 0.96, but specifications should still be verified before use. Check the specifications before using one as a measurement target. The emissivity, wavelength range, and temperature limit all matter. Even the adhesive is a factor. Some thin tapes also let infrared energy pass through instead of fully blocking the surface underneath.

High emissivity labels offer a more permanent option. Their consistent size also helps technicians find the same target during each inspection. That becomes useful when teams compare temperature data over months or years.

A label must be large enough to fill the camera’s measurement spot at the working distance. Seeing the label in the image is not enough. If the measurement area includes both the label and the metal around it, the displayed temperature will be an average of two surfaces.

Apply labels or tape only when the equipment is de-energized and the procedure permits the work. The surface should be clean so that the target stays in place. Once installed, allow it to reach the same temperature as the component before measuring.

High Emissivity Paints and Coatings

Paint works well for a larger target or one that needs to remain in place. Even a small painted patch gives the camera a less reflective surface that emits infrared radiation more consistently.

Flat, nonmetallic paint usually has higher emissivity than glossy or metallic paint. Black is often chosen because it is easy to see, but color alone does not determine thermal performance. A flat white coating may have higher emissivity than a glossy black one.

The coating must be thick enough to block infrared radiation within the camera’s wavelength range. A too-thin layer will allow energy from the material underneath to affect the reading. In high-temperature systems, combustion gases can also influence radiative heat transfer.

High emissivity coatings are also used in high-temperature applications. The product must tolerate the operating temperature, heat cycles, moisture, oil, sunlight, and chemicals at the installation while maintaining consistent radiative heat emission from hot surfaces. In furnace service, high emissivity coatings can improve energy efficiency by 10%. They can also reduce heat-up time by 18%. A coating that cracks or loses adhesion no longer provides a reliable reference.

Very hot equipment may call for a ceramic coating. On an electrical connection, an approved paint dot may be enough. Do not use metallic paint as the measurement target. The metal particles can lower surface emissivity.

Some thermal indicator paints add a visible response. Once a defined temperature is reached, the paint changes color. This gives maintenance teams a quick visual warning along with a high-emissivity surface for thermal imaging.

Choosing Between Materials, Labels, Tape, and Paint

Before choosing a target material, check the component temperature, the area that needs coverage, and how long the target will stay in service.

Tape is quick to install, although its adhesive may soften or dry out over time. Paint takes more preparation and can be difficult to remove, but it may last longer. Labels make the target easy to find as long as they remain clean and firmly attached.

There is no reason to cover an entire component when one properly sized target will do. The camera’s spot-size ratio, lens, inspection distance, and viewing angle determine the area required.

Common Mistakes When Measuring Low-Emissivity Surfaces

The most common mistake is trusting the number on the screen simply because it looks precise. A thermal camera will display a temperature even when much of the infrared radiation came from somewhere else.

Shiny metal is especially troublesome. Polished metals reflect people, nearby machinery, hot pipes, sunlight, and other sources of radiant energy. If an apparent hot area moves when the camera moves, it is likely a reflection.

Another mistake is setting every target to 0.95. That setting may suit a label, piece of tape, or painted surface. It does not represent bare aluminum, copper, or stainless steel.

A target can also be too small. If the camera measures the coating and surrounding metal together, the result will not accurately represent either surface.

Look at the target during every inspection. Paint can chip, tape edges can lift, and oil or dust may cover a label. Any of these changes can affect the reading.

Do not apply coatings to exposed energized components. Target preparation belongs in planned work performed under the facility’s electrical safety procedures.

Best Practices for Improving Infrared Inspection Accuracy

For more consistent temperature measurements:

• Prepare and mark target locations while the equipment is de-energized. Record each location so another technician can find it later.
• Match the camera’s emissivity setting to the label, tape, paint, or coating being measured.
• Enter the reflected temperature separately. If the inspection is performed through an infrared window, include the optic’s transmission value.
• Take the next image from roughly the same position. A change in distance or viewing angle can alter the reading, especially on a small target.
• Record the equipment load with every image. A reading taken under light load should not be compared directly with one taken under heavier operating conditions.
• Check labels, tape, and coatings for dirt, corrosion, lifting edges, or other damage.
• Save the target emissivity, distance, load, reflected temperature, and infrared window transmission with the inspection data.

Frequently Asked Questions

What are high emissivity materials?

High-emissivity targets (e.g., rubber, ceramics, plastic, as well as oxidized metals and matte coatings) throw off a high proportion of their thermal energy and absorb most incoming radiation versus reflecting background heat. Their emissivity numbers stay up near 0.90 or higher, making them much more reliable to scan than bare copper or polished steel. That said, heavy dirt buildup or oil films still alter emissivity enough to diminish measurement accuracy.

What material has the highest emissivity?

Industrial materials do not behave as perfect emitters. Some ceramics, carbon-based surfaces, and matte black coatings can reach emissivity values of 0.95 or higher. Only a theoretical perfect blackbody has the maximum value of 1.

What does high emissivity mean?

A high-emissivity surface gives off most of its available thermal radiation and reflects less energy from nearby objects. At a given temperature, its infrared signal is stronger than the signal from a low-emissivity surface, so reflections have less effect on the temperature measurement.

Is high or low emissivity better for infrared inspections?

High emissivity is usually easier to work with. More of the infrared energy reaching the camera comes from the target surface, so reflections have less influence. Low emissivity does not prevent an inspection, but polished metals may need a prepared label, tape, or painted target. When working outdoors, also account for direct exposure to the sun, as solar radiation can heat external surfaces or create intense background reflections that distort thermal readings.

How do you increase the emissivity of a surface?

Place an approved high emissivity label or tape on the target, or apply a suitable flat paint or coating. Do this while the equipment is de-energized and the work procedure allows it. The selected material must withstand the component’s temperature and operating environment.

What surface emits the most infrared radiation?

Perfect black bodies give off the maximum possible radiation at the same temperature. No actual surface matches it exactly. Some matte black coatings and carbon materials are close, as are ceramics. But their readings shift with temperature and wavelength.

Does aluminum have high or low emissivity?

Bare polished aluminum has low emissivity, from about 0.03 to 0.05. Oxidation, roughening, anodizing, or painting can raise its surface emissivity. For that reason, “aluminum” alone is not enough information for a camera setting. Check the finish before taking a measurement.

Does color affect emissivity?

Visible color will not predict the emissivity of a surface. White paint and black paint in flat finishes can behave much the same way within the infrared range. Look instead at attributes such as: gloss, metallic content, coating thickness, and wavelength. Those details matter more than the surface’s appearance under visible light.

What is high emissivity paint used for?

High-emissivity paint establishes a consistent target area on surfaces that are otherwise difficult to scan. It is commonly applied to polished electrical connections, bare metal housings, piping, and high-temperature process equipment. In furnace and process applications, high-emissivity ceramic coatings are also used to optimize radiative heat transfer. For infrared inspections, however, target paint simply eliminates reflective noise to ensure accurate temperature readings.

When should emissivity labels or tape be used during thermal inspections?

Use emissivity labels or tape when the original surface has low emissivity or its value is uncertain. These also help when the surface changes over time. On shiny metal, the label or tape becomes a fixed target that can be found through an infrared window. For example, a small patch on a shiny can filled with hot water gives the thermal camera a more reliable target than the bare metal surface. Apply it while the equipment is de-energized, then document the location for the next inspection.

Key Takeaways

• High emissivity means more emitted energy reaches the thermal camera and less of the reading comes from reflected radiation.
• Polished metals and other reflective surfaces are easier to check when labels, tape, or paint mark the measurement target.
• Do not choose an infrared emissivity setting by visible color. Check the finish, wavelength, oxidation, and coating composition.
• Note the target size, camera settings, equipment load, and infrared window transmission each time. Without that information, later measurements are harder to compare.

Conclusion

Point a thermal camera at a painted housing, then at the bare connection beside it. The readings may look quite different even when the equipment temperature is the same. Surface condition is the reason.

For reflective targets, labels, tape, and high emissivity coatings give the technician a marked area to check. This is useful when the surface is difficult to characterize, or the same equipment is included on every inspection route.

Plan target preparation for a time when the equipment is open and de-energized. After installing the material, record its location and emissivity. Later inspections can return to the same surface and compare readings under known operating conditions.

Learn more about emissivity in thermal imaging or explore IRISS CAP Series infrared inspection windows for closed-panel thermal inspections.