Difference Between PPGI And PPGL Steel Sheets — 5 Key Insights

Overview

It is important to understand the difference between PPGI and PPGL steel sheets. This knowledge helps manufacturers, builders, and product designers.

They rely on pre-painted coated metals for strength and looks. PPGI (Pre-Painted Galvanized Iron) and PPGL (Pre-Painted Galvalume) are both color-coated steel products. People commonly use them in roofing, wall cladding, home appliances, and transportation.

Even though they look alike, their base coatings, chemical makeup, and performance are different. These differences affect weight, corrosion resistance, lifespan, heat tolerance, and cost.

What Are PPGI and PPGL?

PPGI (Pre-Painted Galvanized Iron Steel) is a type of coated steel that uses a zinc layer as its substrate. They first coat the steel sheet with zinc through hot-dip galvanizing.

This helps prevent rust. Then, they paint it using a continuous coil coating process. This dual-layer protection makes the sheet more resistant to environmental factors. It also gives it a nice look for visible installations.

PPGL (Pre-Painted Galvalume Steel) uses a coating made of aluminum and zinc. This coating usually has about 55% aluminum, 43.4% zinc, and 1.6% silicon. The aluminum in the alloy provides excellent heat and oxidation resistance, while zinc ensures sacrificial protection against corrosion. This unique combination gives PPGL superior durability and longer life compared with traditional galvanized coatings.

PPGI uses a zinc coating. In contrast, PPGL uses an aluminum-zinc alloy coating. This one difference causes all the performance variations.

Substrate and Coating Composition

The type of metallic coating is the primary distinction between PPGI and PPGL steel sheets.

• PPGI has a 100% zinc coating. This coating offers galvanic protection. When it faces moisture or corrosive elements, the zinc corrodes first. This protects the steel underneath.

• PPGL: The aluminum-zinc coating forms a barrier layer that reflects heat and resists corrosion more effectively. The aluminum acts as a passive protective barrier, and the zinc component still offers active sacrificial protection.

This special coating system makes PPGL better for tough and coastal areas. PPGI is still cost-effective and reliable for regular industrial or indoor use.

Weight and Coverage Differences

Weight also distinguishes the two materials. Aluminum is lighter than zinc, which means that for the same coating thickness, PPGL steel sheets weigh slightly less than PPGI sheets. The aluminum-zinc alloy can cover about 3% more surface area than zinc coatings. This is because it has a lower density and spreads better, even with the same coating weight.

This small but important difference can lower material costs and make transportation more efficient. This is especially true for big projects like roofing or cladding systems, where square meter coverage is important.

Service Life and Corrosion Resistance

Service life is one of the most important factors when comparing PPGI vs. PPGL.

For PPGI, the zinc coating provides corrosion protection, but once it starts to degrade, the exposed steel begins to rust quickly. In typical conditions, PPGI can last around 10–15 years depending on coating thickness, paint system, and maintenance frequency.

PPGL, however, performs significantly better. The aluminum-rich coating rusts much slower.

The zinc part gives protection where scratches or edges expose the steel. This synergy allows PPGL to last up to three times longer than PPGI. It typically lasts 25 to 40 years or more when conditions are right.

When projects need to last a long time, PPGL is a better choice. This includes warehouses, energy plants, and marine areas. It may cost a little more, but it is worth it.

Appearance and Surface Finish

While both materials undergo a similar coil coating process, their surface appearance differs noticeably.

PPGI sheets usually have a shiny, metallic finish. In contrast, PPGL sheets have a smoother and slightly matte surface because of the aluminum coating. Aluminum helps the paint stick better to the base metal. This means PPGL may not need as much surface prep as PPGI.

The smooth finish of PPGL makes colored coatings look better. This quality is perfect for high-end building facades and designer roofs.

Heat Resistance and Edge Protection

Heat tolerance is another area where PPGL outperforms PPGI.

The aluminum-zinc alloy coating on PPGL can handle temperatures up to 315°C (600°F). It does not show much discoloration or damage. This makes PPGL ideal for ovens, exhaust pipes, and industrial roofing exposed to high heat or sunlight.

One limitation of PPGL is that its cut edges are less protected. This is because the aluminum-zinc structure does not create a continuous protective film at the edges. In contrast, PPGI’s zinc coating offers better sacrificial protection on cut areas. To prevent localized corrosion, PPGL products used in harsh environments should get edge coating or sealant treatment during installation.

Applications of PPGI and PPGL

Both PPGI and PPGL serve overlapping but distinct market needs:

PPGI is commonly used in:

• Roofing sheets and wall panels for residential and commercial buildings

• Electrical enclosures and appliance bodies

• Interior cladding and decorative panels

• General-purpose industrial sheet metal applications

PPGL is preferred for:

• Roofing and facades in coastal or humid environments

• Solar panel frames and heat-resistant enclosures

• Chimney pipes, HVAC ducts, and oven housings

• Infrastructure requiring long-term, maintenance-free service

In summary, PPGI suits moderate environments, while PPGL is engineered for extreme conditions requiring higher corrosion and heat resistance.

Cost and Market Availability

Price is another key distinction in the difference between PPGI and PPGL steel sheets.

PPGL typically costs 5–15% more than PPGI because of its more complex manufacturing process and superior performance characteristics. Additionally, there are fewer PPGL producers globally compared to PPGI mills, making supply slightly more limited.

Despite its higher price, PPGL offers greater long-term value by reducing maintenance and replacement costs. For clients with extended project lifecycles, the total cost of ownership often favors PPGL.

Working With Quality Coating Suppliers

Whether you choose PPGI or PPGL, partnering with a qualified coating supplier ensures consistent quality. Manufacturers like UNICHEM (Universal Chemicals & Coatings, Inc.) provide high-performance coating technologies designed specifically for pre-painted metals. With over 50 years of experience, they focus on adhesives and coil coatings. These products improve corrosion resistance, color retention, and surface durability for PPGI and PPGL uses.

Working with an experienced coil-coating partner helps ensure proper chemical pretreatment and curing. It also ensures adhesive compatibility. All these factors directly affect the coating's longevity and performance.

Conclusion: Choosing the Right Material

The difference between PPGI and PPGL steel sheets is more than just the coating. It impacts durability, appearance, cost, and long-term performance.

• Choose PPGI when budget is limited and environmental exposure is moderate.

• Choose PPGL when durability, corrosion resistance, and heat tolerance are critical.

Both materials play vital roles in modern architecture and industry. Understanding their unique properties helps you make smarter, cost-effective decisions that align with project requirements.