When selecting a metal building’s roof and wall panels, the coating is more than a finishing touch. It is the first line of defense against years of sunlight, weather, moisture and other environmental exposure.

Two of the most common coating systems used for metal panels are silicone-modified polyester (SMP) and polyvinylidene fluoride (PVDF). Both are proven coating technologies, but they offer different performance characteristics and meet different industry specifications.

Whirlwind Steel now offers both.

WeatherXL™ SMP remains available across our panel gauges, with Cool White remaining available in 24 gauge. Our new Fluropon® 70% PVDF coating is now available on 24-gauge panels, giving customers another option for projects with more demanding coating specifications or long-term appearance requirements.

So, what is the difference between the two?

SMP vs. PVDF: The Basics

SMP stands for silicone-modified polyester. Sherwin-Williams’ WeatherXL™ is an SMP coating system designed for applications including pre-engineered metal buildings, commercial and residential roofing, wall panels, and industrial and agricultural components.

PVDF stands for polyvinylidene fluoride, a fluoropolymer resin used in high-performance architectural coatings. Sherwin-Williams’ Fluropon® 70% PVDF is designed for applications where long-term weatherability, color retention and coating performance are important.

The biggest difference between the two systems is not simply how thick the coating is. It is the resin chemistry behind the coating.

Same Film Thickness, Different Chemistry

Both WeatherXL and Fluropon use a two-coat system consisting of a primer and topcoat. Both have a topside dry film thickness of approximately 0.9–1.1 mils.

That means choosing PVDF does not mean simply putting a thicker layer of paint on the panel.

Instead, the difference comes from the chemistry of the coating itself. That chemistry affects characteristics such as resistance to ultraviolet exposure, color change, chalking and long-term weathering.

PVDF vs. SMP: Side-by-Side

Values shown are requirements under the referenced coating specifications as published by Sherwin-Williams.

Where the Two Coatings Perform Similarly

The comparison is not simply a case of one coating performing while the other does not.

Both SMP and PVDF are established coating systems for exterior metal building applications. Both have requirements for adhesion, impact resistance, pencil hardness, humidity resistance and fire performance. Both also provide options for solar-reflective colors.

That’s why SMP continues to be an important part of Whirlwind Steel’s coating offerings.

WeatherXL SMP remains available across our panel gauges, with Cool White as the exception on 24-gauge panels. This provides a proven coating option for a wide range of agricultural, commercial, industrial and pre-engineered building applications.

Where PVDF Adds Performance

The differences become more noticeable when looking at long-term color and chalk performance and the AAMA specification each coating meets.

A higher AAMA performance specification

Fluropon meets AAMA 2605, while WeatherXL meets AAMA 2604.

AAMA 2603, 2604 and 2605 represent different performance levels for organic coatings, with AAMA 2605 representing the highest of the three specifications.

For projects that specifically call for AAMA 2605 or AAMA 621, Fluropon provides a coating system designed to meet those requirements.

Color and chalk performance

Long-term appearance is one of the primary reasons coating selection matters.

The Fluropon specification calls for no more than 5 Hunter units of color change and a chalk rating of 8 or better at 20 years.

WeatherXL has separate requirements for vertical and non-vertical surfaces, such as roofs. Its specification allows up to 5 ΔE of color change on vertical surfaces and 6 ΔE on non-vertical surfaces, with corresponding chalk requirements.

Salt-spray performance

Laboratory testing also shows a difference in the allowable scribe creep during salt-spray testing.

For Galvalume® or galvanized steel, the Fluropon specification allows up to 1/16 inch of creep from a scribe mark after 1,000 hours. WeatherXL allows up to 1/8 inch.

These standardized tests provide a way to compare coating specifications, but actual performance will always depend on the building, environment, installation and other project conditions.

Why Whirlwind Is Adding PVDF

Whirlwind Steel is now offering Fluropon 70% PVDF on our 24-gauge panels, expanding our coating options for projects where long-term appearance, coating specifications or warranty coverage are particularly important.

Cool White will continue to be available in SMP on 24-gauge panels, while our other 24-gauge color options transition to Fluropon PVDF.

The addition gives customers another coating option for projects where long-term appearance, coating specifications or warranty coverage are particularly important.

Fluropon standard colors on Whirlwind’s 24-gauge panels are backed by a Sherwin-Williams limited warranty that includes:

• 40 years of film integrity
• 30 years for color change
• 30 years for chalking

Terms, conditions and exclusions apply.

Which Coating Is Right for Your Project?

There is no need to view SMP and PVDF as an either-or decision for every building.

WeatherXL SMP remains available across Whirlwind Steel’s panel gauges, including 24 gauge in Cool White, and continues to be a proven option for a wide range of projects. Fluropon 70% PVDF is now available on 24-gauge panels in our new PVDF color offering, providing an option for projects where the coating specification, long-term appearance, warranty requirements or building use call for a PVDF system.

The right coating depends on the project’s specifications, building application, desired appearance, panel gauge and long-term goals.

In Part 1, we covered what PVDF is, what “Kynar” means, and why PVDF coatings are used for demanding exterior applications. But how does PVDF compare to SMP? Both are proven coating systems, but their resin chemistry and performance specifications are different. Here’s what you need to know when comparing Fluropon 70% PVDF and WeatherXL SMP.