Four Essential Types of Injection Molding Surface Finish

In injection molding, both aesthetics and performance are crucial. If a product is directly sold to consumers, its surface treatment not only affects its appearance but also its usability—such as improving scratch resistance, ease of cleaning, or grip. Furthermore, the treatment method also involves cost: high-gloss finishes require more mold polishing, resulting in higher costs; low-gloss finishes are more economical. Therefore, choosing the appropriate surface treatment is a vital decision that balances design aesthetics, performance, and cost control.

What are the plastic finish types?

In the plastics manufacturing industry, the SPI surface treatment standard categorizes product appearance into multiple grades, from glossy to matte finishes, aiming to give products an ideal look and conceal molding defects. More importantly, the SPI standard has become a common technical language in the industry—when design drawings are marked "SPI A-2," the mold shop can accurately understand the required polishing process. This standardized communication significantly improves efficiency from design to manufacturing, and has become a key tool for shortening R&D cycles and reducing design modifications in industries such as consumer electronics and medical devices.

● Shiny Plastic Surface Finish Types

SPI A-1 to A-3 are high-gloss surface treatment grades, all achieved through diamond paste polishing. A-1, in particular, achieves a mirror finish and is commonly found in high-end consumer goods. This type of treatment places extremely high demands on the mold steel used, increasing costs and time, but the resulting natural luster is irreplaceable by subsequent processing.

● Semi-Gloss Plastic Surface Finish Types

The SPI B series (B-1 to B-3) semi-gloss finish is achieved using sandpaper of varying grit, resulting in a moderate gloss level. It balances aesthetics and practicality: providing a textured micro-reflective effect while effectively concealing fingerprints and scratches, making it commonly found in tools, personal care products, and automotive interiors. Its moderate smoothness also promotes durable label and graphic adhesion, making it an ideal choice for both visual quality and durability.

● Matte Plastic Finish Types

Matte surface finishes (SPI C-1 to C-3 grades) are achieved through a fine stone powder polishing process and are commonly used in die-casting and thermosetting parts. Their diffuse reflection properties effectively conceal appearance defects such as parting lines and shrinkage marks, giving complex structural parts a uniform texture. They are widely used in industrial equipment housings, power tools, and other applications where visual imperfections need to be minimized. Simultaneously, the micro-textured surface provides a non-slip grip, making it suitable for scenarios with high tactile safety requirements, such as medical equipment and laboratory tools.

● Dull Plastic Finishes

These surfaces are created using processes like sandblasting and can result in a finish ranging from satin to dull. These are the roughest and least polished grades and are often used for internal parts or for products that require such a finish.

Dull surface finish types are excellent at hiding molding imperfections and have fast cycles. For high-volume parts that customers never see, the speed and simplicity of a dull finish can significantly reduce tooling costs. These parts could be internal brackets, internal clip structures, or hidden frames. For rugged goods, dull finishes are also more forgiving in high-wear environments. The slight abrasions blend in rather than stand out.

Another advantage of dull finishes is that they can provide grip without the need for additional texture processing. Because the surface already has micro-texture from sandblasting, engineers can achieve the “tactile” effect they want without adding texture etching. This makes dull finish types not just an aesthetic choice but a functional one, especially for handheld equipment.

What plastic finish type should I use?

A core principle is that the surface treatment of injection molded parts should be determined by their end use. Is it an appearance part or a structural part? Does it require frequent contact? Clarifying these requirements helps us accurately match the processing techniques in the SPI standard, thereby avoiding rework later and ensuring the value of mold investment. ABBYLEE has extensive experience and can provide you with professional support from solution to mass production. Feel free to contact us anytime to discuss your project needs.