Why Same-Color Comparison Matters When Testing NIR Reflective Coatings

Near-infrared reflective coatings are designed to reflect more solar energy and reduce heat build-up on exposed surfaces. They are used in cool roof coatings, exterior wall paints, coil coatings, industrial finishes, automotive components, marine coatings, coated fabrics and heat-management plastics.

But there is a common problem in laboratory evaluation: two samples are measured for total solar reflectance, near-infrared reflectance or surface temperature even though they do not have the same visible color.

That comparison may produce a number, but it does not necessarily produce a useful conclusion.

A lighter sample will often reflect more incident solar energy than a darker sample. A different colorant can also absorb or transmit near-infrared radiation differently. If the samples are not color-matched, the result may reflect a change in Lab color, pigment package, coating thickness or substrate influence* rather than the true contribution of the NIR reflective pigment.

For coating formulators, R&D teams and purchasing departments evaluating an infrared reflective TiO₂, cool pigment or heat reflective coating additive, the practical rule is simple:

Compare thermal-reflective performance at the same color and under the same application conditions.

What Does “Same Color” Mean in an NIR Reflectance Test?

“Same color” should not mean that two panels look approximately similar under office lighting. It should mean that the visible appearance is measured and controlled using the same color system and agreed tolerance.

The CIE Lab* system is commonly used:

• L* represents lightness, from black to white.
• a* represents the red–green axis.
• b* represents the yellow–blue axis.

A good comparison records L*, a* and b* for every panel. The color difference can then be expressed using a defined equation such as ΔE00, with the acceptance tolerance agreed before testing.

L* is especially important because lightness can strongly influence solar reflectance. However, matching L* alone is not always enough. Two coatings may have almost identical lightness but use colorants with very different absorption behavior in the 700–2500 nm near-infrared region. The full visible color coordinates and the pigment package therefore matter.

This is why a technically valid same-color comparison asks two separate questions:

1. Do the samples have sufficiently similar visible color?
2. At that comparable color, does one formulation deliver higher NIR reflectance or TSR?

Why Color Can Distort NIR and TSR Results

Solar-reflective coating performance is not determined by a single raw material. It is the result of the complete optical system.

1. A Higher L* Can Create an Apparent Reflectance Advantage

White and light-colored coatings generally reflect more visible solar energy than dark coatings. If Sample A is visibly lighter than Sample B, a higher total solar reflectance value for Sample A may be expected even before the functional infrared reflective pigment is considered.

This becomes a serious evaluation error when a conventional TiO₂ formulation is compared with an IR reflective TiO₂ formulation without matching the target color. The test may reward the lighter panel instead of isolating the performance of the infrared reflective material.

2. Different Colorants Behave Differently in the NIR Region

Pigments that create the same visible shade do not necessarily have the same near-infrared absorption. Carbon black is a familiar example: it absorbs strongly across a broad spectral range and can suppress NIR reflectance. Some inorganic color pigments and organic pigments also have distinctive spectral absorption profiles.

Two black, grey, blue, green, red or brown coatings can therefore look similar to the human eye while showing different NIR spectral curves.

This is the working principle behind many “cool color” and non-white solar reflective coatings: the surface maintains the required visible color while the pigment system is designed to absorb less or reflect more energy in the near-infrared region.

3. TSR Includes More Than NIR Reflectance

Total solar reflectance and near-infrared reflectance are related, but they are not interchangeable.

• NIR reflectance focuses on reflectance in the near-infrared wavelength range, commonly evaluated over 700–2500 nm.
• Total solar reflectance (TSR) is a solar-energy-weighted value across a broader portion of the solar spectrum.
• Spectral reflectance shows how the coating behaves at individual wavelengths and helps explain why two similar-looking coatings produce different integrated values.

If the visible colors differ, TSR may change partly because of the visible region. A same-color test reduces that confounding effect and makes the NIR contribution easier to interpret.

The Main Variables That Must Be Controlled

Color matching is necessary, but it is only the first control. A fair NIR reflective coating test should keep the following variables equivalent.

Variable	Why it changes the result	Recommended control
CIE Lab* color	Lightness and hue influence visible and solar reflectance	Record L*, a*, b* and ΔE00; agree the color tolerance in advance
Pigment package	Colorants may absorb, transmit or scatter NIR differently	Use the same colorant family where possible and document every substitution
Resin or binder	Optical clarity, refractive index and film formation affect the coating system	Use the same resin grade and binder-to-pigment ratio
Pigment loading and PVC	Changes scattering, hiding, porosity and film structure	Keep formulation solids and pigment volume concentration controlled
Dispersion	Agglomeration can alter color development and spectral behavior	Use the same equipment, speed, time and dispersion endpoint
Dry-film thickness (DFT)	A thicker film can hide the substrate and increase optical path length	Apply and measure the same DFT rather than relying only on wet-film thickness
Substrate	White, black, metal and transparent substrates reflect or absorb differently	Use the same substrate, primer, surface preparation and orientation
Curing conditions	Film formation and surface texture can change optical response	Control temperature, time, humidity and conditioning period
Surface finish	Gloss, texture and roughness affect reflected light and instrument response	Match gloss and application method where practical
Instrument and method	Geometry, calibration and wavelength range affect reported values	Use the same calibrated instrument, test method and calculation settings
Temperature-test setup	Lamp spectrum, distance, airflow and ambient temperature affect heating	Use a paired setup with identical exposure and report all conditions

A Practical Same-Color Test Workflow

Step 1: Define the Commercial Target

Start with the real application rather than an isolated pigment number. Define:

• target color and color tolerance;
• coating or polymer system;
• required opacity or transparency;
• substrate and primer;
• target dry-film thickness;
• expected outdoor exposure;
• required NIR reflectance, TSR or surface-temperature improvement.

The test for a white cool roof coating is not the same as the test for a dark automotive interior, a colored metal roof or a flexible PVC-coated fabric.

Step 2: Build a Proper Control Formulation

The control should represent the conventional formulation that the new infrared reflective pigment is expected to improve or replace.

Do not compare a carefully optimized NIR reflective coating with an unrelated generic paint. Keep the resin, additives, solids, application process and target color as close as possible. If pigment substitutions are required to achieve color matching, document them clearly.

For low-lightness colors, review the black component carefully. A formulation dominated by conventional carbon black can overwhelm the benefit of an NIR reflective pigment. A controlled carbon-black reduction or composite-black design may be needed, but both the control and test panels must still reach the same approved visual color.

Step 3: Match the Visible Color Before Ranking Thermal Performance

Prepare adjustment panels until the test and control formulations meet the agreed color tolerance. Record the final L*, a*, b*, ΔE00, gloss and opacity.

If the samples are not sufficiently close, treat the result as formulation development data—not as a final product-performance comparison.

Step 4: Apply the Same DFT on the Same Substrate

Dry-film thickness is not a minor detail. A thin coating may allow the substrate to influence the measured reflectance. A thicker coating may provide more complete hiding and a longer optical path.

Use the same applicator, application method, number of coats and curing schedule. Measure the actual DFT on each panel. If substrate influence is part of the research question, test the same formulations on multiple defined substrates rather than mixing substrate effects into one comparison.

Step 5: Measure Color, Spectral Reflectance, NIR and TSR

Use a calibrated UV-Vis-NIR spectrophotometer or an appropriate solar-reflectance instrument. Depending on the project and equipment, recognized methods such as ASTM E903 or ASTM C1549 may be considered.

Report more than one headline number. A useful test record includes:

• L*, a*, b* and ΔE00;
• the full spectral reflectance curve;
• the stated NIR wavelength range and calculation method;
• TSR and the solar weighting method;
• instrument model, measurement geometry and calibration;
• panel DFT, substrate, primer and gloss.

The spectral curve is particularly valuable because it shows where the improvement occurs. Two coatings can have similar integrated values while behaving differently across the wavelength range.

Step 6: Run a Controlled Temperature Comparison

A surface-temperature test can make NIR reflective coating performance easier to understand, but it is highly sensitive to test conditions.

Keep the light source, irradiance, lamp-to-panel distance, exposure time, panel angle, airflow, ambient temperature, backing material and sensor location identical. Test the panels simultaneously where possible. Record both the heating curve and the equilibrium or end-point temperature.

Do not convert one laboratory temperature difference into a universal promise for every roof, wall, vehicle or plastic product. Real application temperature depends on climate, solar intensity, wind, emissivity, insulation, geometry, substrate and heat transfer.

What a Valid Same-Color Result Can Tell You

When the visible color and application variables are controlled, three outcomes become commercially meaningful.

Same Color, Higher NIR Reflectance

This is direct evidence that the formulation reflects more near-infrared energy without requiring a visible color change. It is especially relevant for colored architectural coatings, cool roof coatings, coil coatings, automotive coatings and industrial finishes.

Same Color, Higher TSR

This indicates improved solar-energy reflection across the weighted spectrum. The spectral curve should still be reviewed to understand whether the change is located mainly in the NIR region or elsewhere.

Same Color, Lower Temperature Under Controlled Exposure

This gives application-oriented support for reduced heat build-up. The result is strongest when it is consistent with the NIR and TSR measurements and when all exposure conditions are disclosed.

An IR-1000 Same-Color Application Example

In an ICC flexible-coating evaluation, a formulation containing 5% IR-1000 was compared with a control formulation at almost the same lightness:

Sample	L*	TSR	NIR reflectance
5% IR-1000	40.40	0.35	0.62
Control without IR-1000	40.52	0.30	0.51

Because the L* values were close, the higher NIR reflectance and TSR could be interpreted with much more confidence than a comparison between visibly different samples. The data are application-specific and should not be treated as a universal performance guarantee; resin, colorants, DFT, substrate, dispersion and test method still influence the final result.

This is the real value of same-color testing: it changes a marketing comparison into a formulation decision.

Where IR-600 and IR-1000 Fit

ICC’s IR Series includes two rutile-based infrared reflective titanium dioxide materials for different formulation windows.

IR-600 for White and Light-Color Systems

IR-600 infrared reflective TiO₂ is designed for white, light-color and medium-to-high-lightness coatings and plastics. Typical targets include cool roof coatings, exterior architectural paints, roof and coil coatings, and light-colored plastic systems that require high TSR and NIR performance.

IR-1000 for Colored and Lower-Lightness Systems

IR-1000 infrared reflective TiO₂ is positioned for colored formulations, including lower-lightness systems where the balance between color and heat management is more difficult. Typical applications include colored architectural coatings, metal coatings, industrial coatings, coated fabrics, automotive interiors, marine coatings and solar reflective plastics.

The grade should be selected according to target color, formulation chemistry, film thickness, substrate and performance objective—not by comparing isolated powder reflectance alone.

For formulation data and application reports, visit the IR Series Technical Resources page.

Common Testing Mistakes

• Comparing a lighter NIR coating with a darker control and attributing the full difference to the infrared reflective pigment.
• Matching only L* while ignoring a*, b*, ΔE00 and the spectral behavior of the colorants.
• Applying panels at the same wet-film thickness without verifying dry-film thickness.
• Testing one coating over white card and the other over black, metal or another substrate.
• Using different pigment loadings, PVC, gloss levels or curing conditions.
• Reporting only an infrared-lamp temperature difference without NIR or TSR data.
• Quoting “heat insulation” when the tested mechanism is solar reflection rather than resistance to conductive heat flow.
• Treating powder reflectance as if it were guaranteed finished-coating performance.

Frequently Asked Questions

Why is same-color comparison necessary for NIR reflective coatings?

Because visible color—especially lightness—can change solar reflectance independently of the NIR reflective pigment. Matching the color helps isolate whether the infrared reflective pigment delivers a genuine improvement.

Is matching L* enough?

Not always. L* controls lightness, but a* and b* describe hue direction, and different pigment combinations can have different NIR absorption even at a similar L*. Record the full Lab* values and an agreed color-difference metric such as ΔE00.

What is the difference between NIR reflectance and total solar reflectance?

NIR reflectance focuses on the near-infrared region, while TSR is a solar-energy-weighted value over a broader spectral range. For colored heat reflective coatings, both values and the full spectral curve are useful.

Does higher NIR reflectance always mean a fixed surface-temperature reduction?

No. Higher NIR reflectance can reduce absorbed solar energy, but the final temperature difference depends on the coating, substrate, emissivity, insulation, weather, airflow, geometry and test setup.

Can dark coatings be solar reflective?

Yes. A coating can absorb visible wavelengths to appear dark while using a pigment package that absorbs less or reflects more near-infrared energy. Conventional carbon black usually requires particular attention because it can strongly suppress NIR reflectance.

Does dry-film thickness affect NIR reflectance?

Yes. DFT affects hiding, substrate contribution and the optical path through the coating. Always measure and report the dry-film thickness of both control and test panels.

Why does the substrate matter?

Some coating films transmit part of the near-infrared energy. A white or metallic substrate may reflect transmitted energy back through the film, while a black or absorbing substrate may lower the apparent reflectance. Use the same substrate for direct comparison.

Is heat reflective paint the same as thermal insulation coating?

Not exactly. A solar or infrared reflective coating reduces absorbed radiant energy. Thermal insulation primarily resists conductive heat flow. A coating system may use both approaches, but the mechanisms and test methods are different.

Should I use IR-600 or IR-1000?

IR-600 is generally the better starting point for white and light-color systems. IR-1000 is generally better suited to colored and lower-lightness formulations. Final selection should be confirmed through same-color application testing.

What information should be included when requesting an IR Series sample evaluation?

Provide the target color or Lab* values, resin type, pigment package, current formulation, application, substrate, DFT, curing conditions and the existing NIR, TSR or temperature target. This allows a more relevant test plan to be designed.

Conclusion

The best NIR reflective pigment is not the sample that looks whiter, uses a thicker film or sits on a more reflective substrate. It is the material that provides a measurable NIR, TSR or temperature advantage at the required color and under controlled application conditions.

For a credible comparison, control Lab* color, pigment package, resin, PVC, dispersion, DFT, substrate, curing and measurement method. Then review the spectral curve together with NIR reflectance, total solar reflectance and temperature data.

If you are evaluating a cool roof coating pigment, solar reflective coating, heat reflective paint, colored metal coating or thermal-management plastic, ICC can support grade selection and formulation testing with IR-600 and IR-1000.