An Overview of Injection Molded Surface Finishes
SPI, Mold-Tech, and VDI 3400 injection molding finishes for polished, matte, and textured molded parts.
Injection Molding Service
Choosing the Right Finish for Your Injection Molded Parts
A common question we hear is: "What do your molded parts look like?" The answer is: however you want. We have access to a diverse marketplace of molding suppliers and all standard mold finishing options. Our mold finishes include SPI, MoldTech, VDI (EDM), and others. Finishes can range from glossy to matte to patterned. Finishes applied to the surface of the mold cavity transfer to the surface of the molded part—for example, a polished mold surface produces a reflective or transparent part. Mold finishes are different from finishes for CNC machined or 3D printed parts, where each component is treated individually. Adding a finish or texture can change the tool's price depending on the process required, but it does not alter the price of the individual parts.
The most common finishes are from the Society of the Plastics Industry (SPI): standard mold finishes from heavily polished (SPI A) to semi-gloss (SPI B) to fine and coarse matte (SPI C and SPI D). Polished textures can increase cosmetic reflection or transparency on transparent polymers; matte finishes can provide subdued tones and help prevent fingerprints on handled products.
Society of Plastics Industry (SPI) Mold Finishes
Standard SPI injection molding finishes
| SPI Finish | Description | Typical Applications | Surface Roughness (Ra µm) |
|---|---|---|---|
| SPI A-1 | Grade #3, 6000 Grit Diamond Buff | High polish or transparent parts, optically clear | 0.012 - 0.025 |
| SPI A-2 | Grade #6, 3000 Grit Diamond Buff | High polish or transparent parts | 0.025 - 0.050 |
| SPI A-3 | Grade #15, 1200 Grit Diamond Buff | High-to-medium polish parts, non-optical lenses | 0.050 - 0.100 |
| SPI B-1 | 600 Grit Paper | Medium polish parts | 0.05 - 0.10 |
| SPI B-2 | 400 Grit Paper | Medium polish parts | 0.10 - 0.15 |
| SPI B-3 | 320 Grit Paper | Medium - low polish parts | 0.28 - 0.32 |
| SPI C-1 | 600 Stone | Low polish parts | 0.35 - 0.40 |
| SPI C-2 | 400 Stone | Low polish parts | 0.45 - 0.55 |
| SPI C-3 | 320 Stone | Low polish parts | 0.63 - 0.70 |
| SPI D-1 | Dry Blast Glass Bead | Satin finish | 0.80 - 1.00 |
| SPI D-2 | Dry Blast #240 Oxide | Dull finish | 1.00 - 2.80 |
| SPI D-3 | Dry Blast #24 Oxide | Dull finish | 3.20 - 18.00 |
Mold-Tech Textured Finishes
Mold-Tech is a standardized mold texturing option typically used for commercial or saleable goods, serialized in series A through D. Series A is most common—fine to coarse matte finishes that do not require laser, masked chemical etching, or other engineered texturing. Texture is categorized by serial number and texture depth. Add 1.5° of draft for every 0.001" of texture depth (more aggressive draft than SPI).
Mold-Tech A Finishes
| Mold-Tech Serial | Texture Depth | Application | Minimum Draft |
|---|---|---|---|
| MT-11010 | 0.001" | Dull matte finish | 1.5° |
| MT-11020 | 0.0015" | Coarse matte finish | 2.25° |
| MT-11030 | 0.002" | Coarse matte finish | 3° |
VDI (EDM) Mold Texture Values
VDI 3400 (Verein Deutscher Ingenieure—Society of German Engineers) is an international standard for mold texturing of matte surfaces, mainly processed by Electrical Discharge Machining (EDM). The EDM surface gives a fine-to-coarse grain. Some textures have near equivalencies: e.g. SPI D-3, VDI 33, and MT-11020 look very similar; VDI 12 and SPI C-1 are equivalent.
| VDI Value | Description | Applications | Ra (µm) |
|---|---|---|---|
| VDI 12 | 600 Stone | Low polish parts | 0.40 |
| VDI 15 | 400 Stone | Low polish parts | 0.56 |
| VDI 18 | Dry Blast Glass Bead | Satin finish | 0.80 |
| VDI 21 | Dry Blast # 240 Oxide | Dull finish | 1.12 |
| VDI 24 | Dry Blast # 240 Oxide | Dull finish | 1.60 |
| VDI 27 | Dry Blast # 240 Oxide | Dull finish | 2.24 |
| VDI 30 | Dry Blast # 24 Oxide | Dull finish | 3.15 |
| VDI 33 | Dry Blast # 24 Oxide | Dull finish | 4.50 |
| VDI 36 | Dry Blast # 24 Oxide | Dull finish | 6.30 |
| VDI 39 | Dry Blast # 24 Oxide | Dull finish | 9.00 |
| VDI 42 | Dry Blast # 24 Oxide | Dull finish | 12.50 |
| VDI 45 | Dry Blast # 24 Oxide | Dull finish | 18.00 |
Default Finish & Options
Unless otherwise specified, an injection molded part will typically have an SPI B-2 default finish to enable better part release from the mold and remove tool marks. Surface finishes can be applied to some or all faces—for example, an opaque part can have a custom outer surface while the interior, non-cosmetic surface remains default. Multiple finishes and texturing can be applied to a single tool cavity if required. Transparent parts are typically polished on both sides for highest clarity.
We offer a wide variety of surface finishes and additional mold textures so your parts meet all structural and cosmetic requirements.