When you are sourcing prepainted galvanized steel (PPGI) coil, the gloss level is often the first specification a buyer asks about, yet it is also one of the most misunderstood. In simple terms, a gloss level of 20 is a matte finish, 40 is a semi-gloss, and 70 is a high-gloss finish. The right choice is not about which number looks better on paper; it is about matching the finish to your specific climate, forming process, application, and budget. This article explains the practical differences between PPGI gloss levels 20, 40, and 70 in terms of aesthetics, durability, and cost, so you can specify the correct product for your next project.
What Does the Gloss Level Number Actually Mean?
The gloss level is a measurement of light reflection from the coil surface, typically measured with a glossmeter at a 60-degree angle. A lower number means the surface scatters light more, resulting in a flatter, less shiny appearance. A higher number means the surface reflects light more directly, appearing brighter and more mirror-like.
This is a physical property of the paint film, not just a visual preference. The gloss level is determined by the type of resin system used, the amount of matting agent added to the paint, and the finishing process. You cannot simply adjust the gloss of a finished coil without changing the paint formulation, which is why the gloss level must be specified before production begins.
Standard Gloss Ranges in the Industry
While you may specify any number, the industry generally standardizes around three tiers:
- Gloss 20 (Matte): Typically ranges from 15 to 25 units. This is a low-sheen surface that minimizes light reflection.
- Gloss 40 (Semi-Gloss): Typically ranges from 35 to 45 units. This is a middle ground, offering a soft sheen without being overly shiny.
- Gloss 70 (High-Gloss): Typically ranges from 65 to 75 units. This is a bright, reflective surface that provides a “wet look.”
It is critical to understand that a gloss range, not a single number, is the industry norm. If you write “Gloss 40” on your RFQ, a supplier will generally produce coil within a +/- 5 unit tolerance. Confirm the acceptable tolerance range with your supplier, as this affects color consistency across different batches.
Gloss 20: The Matte Finish for Industrial and Architectural Durability
Matte finishes are the preferred choice for many industrial applications, but they are increasingly popular in modern architecture for their understated elegance.
Advantages of Gloss 20
- Scratch and Mar Resistance: A matte surface hides minor scratches, scuffs, and fingerprints far better than a glossy surface. This is a major advantage during handling, roll forming, and installation.
- Reduced Glare: For roofing and cladding in sunny regions, a low-gloss surface reduces light reflection, which can be a nuisance for neighboring buildings and a safety hazard for pilots or drivers.
- Hides Surface Imperfections: Matte finishes are more forgiving of minor substrate irregularities or slight variations in the paint film that might be visible under a glossy reflection.
Disadvantages of Gloss 20
- Color Retention Perception: Matte finishes can appear slightly duller in color over time as they are more prone to collecting dirt and atmospheric pollutants, which can make the surface look gray unless cleaned regularly.
- Cleaning Difficulty: The textured micro-surface of matte paint can trap dirt more easily than a smooth glossy surface, requiring more effort to clean.
Best Use Cases: Industrial roofing, agricultural buildings, internal wall cladding in workshops, and architectural projects seeking a modern, non-reflective aesthetic. If your project is in a polluted or dusty environment, a matte finish may require more maintenance to keep its appearance.
Gloss 40: The Versatile Semi-Gloss for General Construction
Semi-gloss is the default specification for a vast range of construction and appliance applications. It offers a balance between the practical benefits of matte and the aesthetic appeal of high-gloss.
Advantages of Gloss 40
- Balanced Aesthetics: It provides a clean, vibrant appearance without the harsh glare of high-gloss. It is often perceived as a “professional” finish that works well in both commercial and residential settings.
- Good Formability: Semi-gloss formulations are widely used and well understood by coil coaters. They generally offer excellent flexibility, making them suitable for complex roll-formed profiles without cracking the paint film.
- Ease of Maintenance: The smoother surface of a semi-gloss finish is easier to clean than matte, and it does not show water spots or streaks as easily as high-gloss.
Disadvantages of Gloss 40
- Visibility of Defects: While better than high-gloss, a semi-gloss finish will still reveal minor surface defects, such as “orange peel” or slight dents, more readily than a matte finish.
- Compromise: It is a compromise. You do not get the maximum glare reduction of matte, nor the maximum “pop” of high-gloss.
Best Use Cases: Roofing sheets, wall cladding for warehouses and factories, residential roofing, garage doors, and light structural sections. If you are unsure which gloss to choose, Gloss 40 is the safest starting point for most general construction applications.
Gloss 70: The High-Gloss Finish for Maximum Visual Impact
High-gloss finishes are chosen for their vibrant color depth and reflective properties. They are common in applications where aesthetics are the primary driver.
Advantages of Gloss 70
- Superior Color Depth: High-gloss paints reflect more light, making colors appear richer, deeper, and more saturated. This is ideal for brand-colored buildings or architectural statements.
- Smooth Surface: The high-gloss finish is typically achieved with a smoother paint film, which is more resistant to dirt adhesion and easier to wash down.
Disadvantages of Gloss 70
- High Visibility of Defects: Any scratch, dent, or forming mark will be magnified under the reflective surface. This increases the risk of rejection during installation and requires careful handling.
- Forming Challenges: High-gloss films can be more brittle and prone to micro-cracking during severe bending or roll forming. They require more precise tooling setup.
- Glare Issues: In direct sunlight, high-gloss roofing can create significant glare, which may be unacceptable in certain urban or airport-adjacent zones.
Best Use Cases: Decorative wall panels, entrance canopies, household appliance panels, and commercial signage. It is generally not recommended for roofing in high-sun-exposure regions due to glare and thermal expansion considerations.
Practical Decision and Specification Table
Use this table as a quick reference when preparing your specification. Remember that actual performance depends on the specific paint system (e.g., polyester vs. PVDF) and the substrate.
| Specification | Gloss 20 (Matte) | Gloss 40 (Semi-Gloss) | Gloss 70 (High-Gloss) |
|---|---|---|---|
| Light Reflection | Low | Medium | High |
| Scratch Visibility | Low (Hides well) | Medium | High (Shows easily) |
| Dirt Retention | High (Traps dirt) | Medium | Low (Smooth surface) |
| Color Vibrancy | Dull/Flat | Good | Excellent |
| Typical Formability | Good | Excellent | Fair to Good |
| Glare Risk | None | Low | High |
| Common Use | Industrial, Agricultural | General Construction | Decorative, Appliances |
| Relative Cost Driver | Standard | Standard | Premium (due to higher QC and resin cost) |
How Gloss Level Impacts Cost and Durability
You might assume that higher gloss means higher cost. While this is often true, the cost driver is not the gloss itself but the resin system required to achieve it.
Cost Drivers
High-gloss finishes generally require premium resin systems (like certain polyesters or PVDF) to maintain their shine without chalking or fading. These resins are more expensive. Additionally, high-gloss lines require stricter quality control to avoid surface defects, which can increase production waste and, therefore, the unit price. Matte finishes can sometimes be achieved with lower-cost resin formulations, but this is not guaranteed.
To get an accurate cost comparison, you must request a dated quote for the same substrate, coating thickness, and color in all three gloss levels. Do not assume a linear price increase; the difference between Gloss 40 and Gloss 70 is often larger than between 20 and 40.
Durability Considerations
In terms of durability, gloss level alone does not determine lifespan. A high-gloss polyester will not outlast a matte PVDF. Durability is dictated by the resin chemistry (e.g., SMP, HDP, PVDF), the primer system, and the metallic coating weight of the underlying GI coil. However, gloss level does affect aesthetic durability. High-gloss surfaces fade and chalk more visibly over time if the wrong resin is used. Matte surfaces may show chalking less, but they can become permanently stained by dirt if not cleaned.
Actual performance depends on substrate, metallic coating, paint system, environment, forming and maintenance. Always specify the paint system and the expected environmental exposure (UV index, salinity, pollution) when requesting a quote.
Common Mistakes When Specifying Gloss
Avoid these frequent errors to prevent costly production delays and material rejection:
- Specifying a single number without a tolerance: Always specify a range (e.g., Gloss 40 +/- 5). Expecting a precise “40.0” reading is unrealistic.
- Choosing gloss for aesthetics only: Failing to consider the roll-forming process. A complex profile with tight bends may crack a high-gloss film. In such cases, a semi-gloss or matte with higher flexibility is required.
- Ignoring the paint system: Requesting “Gloss 70” without specifying the resin (e.g., SMP vs. HDP) is dangerous. A Gloss 70 SMP will chalk and fade much faster than a Gloss 40 HDP. The gloss level is not a proxy for quality.
- Mixing gloss levels in one project: Even from the same supplier, a Gloss 20 and a Gloss 40 from different production batches will look different. If you need to match existing panels, you must supply a physical sample or a precise color code and gloss range.
RFQ Checklist for Gloss and Quality
When you contact a supplier, ensure your RFQ includes the following to avoid ambiguity:
- Base Metal: Specify the substrate, e.g., GI coil or Galvalume, and the required metallic coating weight (e.g., Z120, Z275).
- Paint System: Specify the resin type (Polyester, SMP, HDP, or PVDF) and the paint film thickness (e.g., 20/5 microns or 25/8 microns).
- Gloss Level: State the target gloss and the acceptable tolerance (e.g., Gloss 40 +/- 5 units at 60 degrees).
- Color Code: Provide a RAL number, a Pantone code, or a physical sample. State that the final color must be matched under standard lighting conditions.
- Forming Method: Describe the profile (e.g., corrugated, standing seam) and the minimum bending radius. This helps the supplier advise on gloss and resin flexibility.
- Standard: If you require compliance with a standard like ASTM or EN, name the specific standard and edition. Confirm the required edition and exact contract values with the supplier, as standards are updated periodically.
- Intended Use: State whether this is for roofing, wall cladding, or an appliance. This informs the UV and corrosion resistance requirements.
Frequently Asked Questions
Can I use Gloss 70 for roofing in a coastal area?
You can, but it is not recommended. The high gloss will show the effects of salt spray and UV degradation more visibly. For coastal areas, a lower gloss (20 or 40) with a PVDF or high-durability polyester resin is a more prudent choice for long-term aesthetics.
Does a matte finish (Gloss 20) last longer than a high-gloss finish?
Not necessarily. The lifespan is determined by the resin system and the environment, not the gloss level. A matte finish will hide scratches and chalking better, making it look better for longer in high-handling environments. However, a high-gloss PVDF can outlast a matte polyester in terms of color retention.
Is Gloss 40 the cheapest option?
Generally, yes. Gloss 40 is the most widely produced specification, so it benefits from economies of scale. Gloss 20 can sometimes require specific matting agents that add cost, and Gloss 70 often requires premium resins. However, confirm this with a dated quote, as pricing fluctuates with raw material costs.
How do I measure the gloss level of a sample?
Use a glossmeter set to a 60-degree angle. Place the device flat on the surface and take several readings across the panel. The average of these readings is the gloss level. Ensure the panel is clean and flat before measuring.
Can I get a color match in a different gloss level?
Yes, but the color will appear slightly different. The same pigment will look lighter and less saturated in a matte finish and darker and more vibrant in a high-gloss finish. Your supplier will need to adjust the pigment formulation to achieve the same visual color perception across different gloss levels.
Making the Final Decision
There is no universally “best” gloss level. The correct specification balances the physical demands of your forming process, the environmental exposure of the final product, and the visual expectations of your customer.
For a standard roofing profile in a moderate climate, Gloss 40 is the industry workhorse. For industrial sheds where handling damage is common, Gloss 20 is the practical choice. For architectural panels where appearance is paramount and handling is controlled, Gloss 70 offers the most striking finish.
Before finalizing your order, review our detailed guide on PPGI coil specifications to understand how gloss interacts with other quality parameters. Remember that the gloss reading is just one line in a complex specification sheet. A good supplier will ask you about your forming equipment and final application before confirming the gloss level, not just quote the number you wrote down.
Request a Specification Review
Choosing a gloss level is a technical decision, not a sales decision. If you are uncertain about the best finish for your specific profile, climate, and budget, we are happy to review your requirements. Send us your profile drawings, your intended application, and your target gloss level, and we will provide technical feedback on the feasibility and cost implications.
Contact our technical sales team via the ChinaCNU contact page with your RFQ checklist completed. We will respond with a dated quotation and a specific recommendation for your project, ensuring you get the right balance of aesthetics, durability, and cost.
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