Injection Molded Parts Surface Finish: SPI VS VDI — What’s the Difference?

When it comes to custom injection molded parts, surface finish matters — not just for appearance, but also for functionality and user experience. Among the most commonly used surface finish standards are SPI and VDI. But what exactly are they, and how should you choose between them? Let’s break it down

SPI Surface Finish Standard (Defined by the Society of the Plastics Industry, USA)

The SPI standard focuses on polish level, often used to define the smoothness or glossiness of the mold surface. Common categories include:

A Series (High Gloss Polish): Mirror-like, high-gloss surfaces, ideal for transparent or premium aesthetic parts.

B Series (Semi-Gloss Polish): Medium polish using finer sandpaper, suitable for general-purpose applications.

C Series (Matte Finish): Coarser sanding, low gloss, more functional in appearance.

✅ Best for: Parts that require high reflectivity or smooth finishes, such as cosmetic packaging, medical devices, or clear components.

VDI Surface Finish Standard (Defined by the German Association of Engineers)

VDI standard refers to mold texture (etching) levels, typically used to create matte or textured surfaces. Grades like VDI 12, VDI 18, VDI 24, VDI 28, etc., represent increasing levels of roughness — the higher the number, the rougher the texture.

✅ Best for: Applications that require uniform texture, anti-slip surfaces, or specific tactile design, such as automotive interior parts, handheld devices, and industrial enclosures.

SPI vs VDI — A Quick Comparison

VDI Parameters:

SPI polish grade：

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