In this guide, you’ll find everything you need to know about SPI Finish.
The VDI 3400 and SPI Finish are the two most widely used surface finishes for plastic injection molds. They consist of 90% of finish references on the market.
SPI Finish provides a fast and straightforward solution for mold polishing and sandblasting.
SPI Finish (SPI Finishes) is also known as “SPI Mold Finish (SPI Mold Finishes)” or “SPI Surface Finishes“.
The SPI Finish refers to the American surface finish standard set by SPI (Society of the Plastics Industry). The standard covers 12 SPI grades of polish finishes: SPI A1 to #SPI D3 (RA 0.012 μm to RA 18.00μm).
Although the Society of the Plastic Industy set SPI Mold Standard, it is widely used by mold makers, industrial designers, and marketers worldwide. That’s to say, it is not just an American standard but also a global mold finish standard. If you work with your off-shore molders, for example, in China, you may still use the same standard for mold polish request.
If you want to see what physical plastic samples of SPI mold finish would look like, you may jump to SPI Finish Card section.
There are a few finishing methods to get the 12 SPI finish grades.:
The complete SPI finish standard covers 12 grades from SPI A1 to D3.
At below SPI finish chart, we use surface roughness Ra (μm), finishing methods, recommended steels as references to show each grade’s finish.
If you want to check what the physical textures look like, the best way is to get our SPI Finish card.
| SPI Finish Standard | Surface Roughness Ra in µm | Finishing Method | Fnishing Look | Steels Recommended |
|---|---|---|---|---|
| SPI A1 | 0.012 to 0.025 | 6000 Grit Diamond | Super High Glossy finish | S136 (54HRC) or 8407(52HRC) |
| SPI A2 | 0.012 to 0.025 | 3000 Grit Diamond | High Glossy finish | S136 (54HRC) or 8407(52HRC) |
| SPI A3 | 0.05 to 0.10 | 1200 Grit Diamond | Normal Glossy finish | S136 (300HB) or 718H |
| SPI B1 | 0.05 to 0.10 | 600 Grit Paper | Fine Semi-glossy finish | 718H |
| SPI B2 | 0.10 to 0.15 | 400 Grit Paper | Medium Semi-glossy finish | 718H |
| SPI B3 | 0.28 to 0.32 | 320 Grit Paper | Normal Semi-glossy finish | 718H |
| SPI C1 | 0.35 to 0.40 | 600 Grit Stone | Fine Matte finish | 718H |
| SPI C2 | 0.45 to 0.55 | 400 Grit Stone | Medium Matte finish | 718H |
| SPI C3 | 0.63 to 0.70 | 320 Grit Stone | Normal Matte finish | 718H |
| SPI D1 | 0.80 to 1.00 | Dry Blast Glass Bead | Satin Textured finish | 718H |
| SPI D2 | 1.00 to 2.80 | Dry Blast | Dull Textured finish | 718H |
| SPI D3 | 3.20 to 18.0 | Dry Blast | Rough Textured finish | 718H |
Plastopia provides a plastic SPI Finish card at palm-size to give you a useful guide on SPI Finish Standard.
Compared with traditional metal plaques, plastic cards give you a real hand touch or visual polish finish of your plastic parts. You will see what you will finally mold.
The card comes with 16+ different plastic materials and colors for your wide selection: from commodity plastics (ABS, PP, and others) to engineering plastics (HIPS, PA+GF30, and others). We also provide customization if required.
We designed our SPI finish card at a palm-size of 160×65×2 mm for easy carrying. You can bring it to any production site or even at a customer’s meeting. The card has two sides and comes with the 12 SPI finish grades from A1 to D3.
Here is the picture of Side A. From left to right: SPI A1, SPI A2, SPI A3, SPI B1, SPI B2, and SPI B3 (Each plaque is at 40×20 mm.)
And here is the picture of Side B. From left to right: SPI C1, SPI C2, SPI C3, SPI D1, SPI D2, and SPI D3 (Each plaque is at 40×20 mm.)
Check out our unboxing video below to learn more details:
Plastopia’s SPI Finish cards are already trusted and widely used by major brand companies like Apple, Samsung, Canon, Meta, Space-X, and many more.
Here is the conversion form from the SPI finish (SPI Mold Finish) to RA values.
| SPI Finish Standard | Surface Roughness Ra (μm) |
|---|---|
| SPI A1 | 0.012 to 0.025 |
| SPI A2 | 0.012 to 0.025 |
| SPI A3 | 0.05 to 0.10 |
| SPI B1 | 0.05 to 0.10 |
| SPI B2 | 0.10 to 0.15 |
| SPI B3 | 0.28 to 0.32 |
| SPI C1 | 0.35 to 0.40 |
| SPI C2 | 0.45 to 0.55 |
| SPI C3 | 0.63 to 0.70 |
| SPI D1 | 0.80 to 1.00 |
| SPI D2 | 1.00 to 2.80 |
| SPI D1 | 3.20 to 18.0 |
VDI 3400 standard is mainly a reference for surface roughness (focus on “ROUGH”). SPI Finish is mostly for mold polish (focus on “SMOOTH”).
Although they are made for different surface finishes, they still share some close finishes based on varied grades. Below is the form of SPI to VDI 3400 if you need a rough match.
If you want to check the difference in physical plastic parts, we provide both the VDI 3400 card and SPI finish card in 11 types of plastics. You can compare and decide the surface finish you need. Check here.
| SPI Finish Standard | VDI 3400 Standard | Roughness (RA/ micrometer) | Typical Finishes |
|---|---|---|---|
| SPI A1 | Not Available | 0.012 to 0.025 | Lens / Mirror |
| SPI A2 | Not Available | 0.025 to 0.05 | High Polish |
| SPI A3 | VDI #0 ~ #5 | 0.05 to 0.10 | High Polish |
| SPI B1 | VDI #6 | 0.05 to 0.10 | Medium Polish |
| SPI B2 | VDI #7 ~ #8 | 0.10 to 0.15 | Medium Polish |
| SPI B3 | VDI #9 ~ #10 | 0.28 to 0.32 | Medium- Low Polish |
| SPI C1 | VDI #11 ~ #12 | 0.35 to 0.40 | Low Polish |
| SPI C2 | VDI #13 ~ #15 | 0.45 to 0.55 | Low Polish |
| SPI C3 | VDI #16 ~ #17 | 0.63 to 0.70 | Low Polish |
| SPI D1 | VDI #18 ~ #19 | 0.80 to 1.00 | Satin Finish |
| SPI D2 | VDI #20 ~ #29 | 1.00 to 2.80 | Dull Finish |
| SPI D3 | VDI #30 ~ #45 | 3.20 to 18.0 | Dull Finish |