If you’re specifying or purchasing metal roofing and building panels, solar reflectivity has quickly become a must-understood performance metric. Whether your project is in a hot, sunny climate or part of a sustainability initiative, choosing the right materials can impact thermal comfort, energy use, long-term durability, and cost savings.

At Mill Steel, our stocked inventory includes Sherwin Williams WeatherXL and Akzo Nobel Ceram-A-Star 1050 coatings. The Solar Reflectivity Index (SRI) data sheets for these popular SMP (Silicon Modified Polyester) coatings help you compare performance and select the right product for your building’s needs.

Click here for the Sherwin-Williams Solar Reflectivity Sheet

Click here for the Akzo Nobel Solar Reflectivity Sheet

What Is Solar Reflectivity?

Solar reflectivity (sometimes referred to as “reflectance”) is the ability of a surface to reflect solar energy back into the atmosphere instead of absorbing it. It’s a key part of what makes a roof “cool.”

A highly reflective surface:

Reflects more sunlight
Absorbs less heat
Helps lower surface temperature. This directly affects building energy loads.

The Smart Surfaces Coalition offers a great introduction to solar reflectivity and the impact of surface performance. This solar reflectivity guide from The Cool Roof Rating Council is also a great resource.

Breaking Down the Values: TSR, SR & SRI Explained

When reviewing solar reflectivity data sheets, you’ll typically see three key measurements: TSR, SR, and SRI. While they’re related, they measure different aspects of thermal performance. Understanding the difference helps buyers and specifiers make informed decisions for metal roofing and building systems.

SR = Solar Reflectance

Solar Reflectance (SR) measures the percentage of solar energy a surface reflects away.

Expressed as a value between 0 and 1 (or sometimes as a percentage)
Higher numbers mean more sunlight is reflected
Lighter colors typically have higher SR values

For example, a roof panel with an SR of 0.70 reflects 70% of incoming solar radiation and absorbs the remaining 30%.

In metal roofing, SR is often the first metric referenced when discussing cool roofing performance.

TSR = Total Solar Reflectance

Total Solar Reflectance (TSR) is very similar to SR but accounts for reflection across the entire solar spectrum — including visible light, infrared, and ultraviolet wavelengths.

Why it matters:

Some coatings reflect infrared light extremely well — even if the visible color is darker.
Modern pre-painted PVDF (Kynar®) and SMP (Silicon Modified Polyester) coated steel can incorporate “cool pigment” technology to improve TSR without dramatically changing appearance.

TSR is especially useful when evaluating mid-tone or darker metal roofing colors that are engineered for higher performance than they appear.

SRI = Solar Reflectance Index

Solar Reflectance Index (SRI) combines two properties:

Solar Reflectance (SR)
Thermal Emittance (the ability of a surface to release absorbed heat)

SRI provides a more complete picture of how hot a surface will get in the sun.

Calculated on a scale typically from 0 to 100+
Higher SRI = cooler surface temperature
Some high-performance materials can exceed 100

While SR tells you how much sunlight is reflected, SRI tells you how hot the roof will actually become under real-world conditions.

This is why building codes, LEED credits, and cool roofing standards often reference SRI values rather than SR alone.

Why These Values Matter in Metal Roofing Selection

When comparing:

PVDF (Kynar®) coated steel
SMP coated steel
Reflective aluminum

You’re not just comparing color — you’re comparing long-term performance.

Higher SR and TSR values help reduce solar heat gain.
Higher SRI values indicate lower rooftop surface temperatures.
Better coatings maintain these values longer over time.

For buyers specifying metal roofing systems in commercial, industrial, agricultural, or municipal projects, reviewing TSR, SR, and SRI together ensures:

Energy efficiency targets are met
Cool roofing requirements are satisfied
Sustainability certifications are supported
Long-term performance expectations align with project goals

Solar Reflectivity + Cool Roofing: What’s the Connection?

“Cool roofing” refers to roofing systems designed to:

Reflect more sunlight
Emit absorbed heat more efficiently

Systems that perform well on these criteria maintain lower rooftop temperatures, which can reduce:

Cooling energy use
HVAC demand
Heat stress within the building

Metal panels naturally lend themselves to cool roofing, especially when coated with high-performance paints like PVDF (Kynar) or SMP — which can retain reflectivity longer than basic finishes.

Why Solar Reflectivity Matters in Metal Roofing

Metal roofing isn’t just long-lasting and recyclable — it’s also one of the best platforms for controlled reflectivity thanks to quality pre-painted coatings.

Here’s why specifiers care:

1. Energy Savings & Sustainability

Higher reflectivity = less solar heat gain → lower building interior temperatures → reduced air conditioning load. That translates into measurable operational energy savings.

This is especially important in:

Schools
Warehouses & distribution centers
Retail facilities
Manufacturing plants

For net-zero and high-efficiency projects, reflectivity performance can also contribute to LEED, ENERGY STAR®, and other green building credits.

2. Occupant Comfort

In unconditioned spaces, or buildings with rooftop work areas, lower surface temperatures create a more comfortable environment for occupants.

3. Roof Longevity & Performance

Excessive heat accelerates material degradation. Cool metal roofing systems with high solar reflectivity can reduce thermal cycling stress and prolong panel life.

4. Climate & Regional Efficiency

Solar reflectivity matters more in warmer, sunnier climates, but it still has value pretty much everywhere energy cost is a factor.

Coatings That Boost Reflectivity: PVDF, SMP & Reflective Aluminum

Not all finishes are created equal when it comes to solar reflectivity and long-term performance.

PVDF (Kynar®) Coated Steel

Industry benchmark for long-term color and reflectivity retention
Excellent resistance to chalking and fading
Performs well in cool-roof applications

SMP (Silicon Modified Polyester) Coated Steel

Cost-effective balance of performance and durability
Good reflectivity retention for many commercial projects
Great option where budgets are tighter, but performance is still required

Reflective Aluminum

Ultra-high reflectivity, especially in natural or lightly tinted finishes. Aluminum’s inherent brilliance often yields some of the highest solar reflectivity values, making it an ideal choice for:

Buildings seeking maximum passive cooling benefit
Projects where reflective performance is prioritized over color

Industries & Applications Using Cool Metal Roofing

Solar reflective metal roofing is popular across a range of industries and building types:

Where Solar Reflectivity Comes into Play

New construction metal buildings
Retrofits / reroofs seeking performance upgrades
Sustainable or code-driven projects (e.g., municipal cool roof ordinances)
High energy-cost regions looking for ROI through efficiency

Frequently Asked Buyer Questions

Q: What SRI values should I target for cool roofing?

A: That depends on your climate and project goals. Generally, higher SRI means lower heat gain, and cool roof codes often reference minimum SRI values.

Q: How do coatings affect reflectivity over time?

A: Paint systems like PVDF (Kynar) hold reflectivity longer than basic coatings. That’s why premium pre-painted steel performs better over decades.

Q: Does color matter?

A: Yes — lighter colors typically have higher reflectivity. But modern PVDF and SMP formulations can bring surprisingly good performance even in mid-tone hues.

Internal Resources You May Find Helpful

To support your planning and specification process, check out other Mill Steel articles:

Linking these resources helps you explore material selection from coating to structural performance.

Final Takeaways

Solar reflectivity is a measurable property that affects energy performance, occupant comfort, roof longevity, and sustainability outcomes. In metal roofing and building systems, the choice of coatings — from PVDF (Kynar®) to SMP and reflective aluminum — directly influences reflective performance.

Make decisions backed by data. Use the solar reflectivity sheets, and partner with knowledgeable suppliers like Mill Steel to ensure your metal building meets your requirements and performs well into the future.

Check out our painted coil stock options or contact a Mill Steel expert today for assistance in specifying the right product for your job.

Solar Reflectivity Explained: Buyer’s Guide to Cool Roofing Performance