In the field of injection molding, mold surface textures directly determine the appearance, feel, functionality, and cost of plastic parts. Clients often ask: “We want matte/frosted/mirror/leather/grain/sandblast—which standard should we use?”
The three most commonly used global standard systems are:
- SPI (Society of Plastics Industry standard, now Plastics Industry Association)
- VDI 3400 (German Engineers Association standard, commonly used for EDM spark-eroded textures)
- Mold-Tech (commercial texture standard from the U.S. company Mold-Tech, abbreviated as MT)
Below is a clear breakdown of the common grades in these three systems, including corresponding roughness values, appearance characteristics, typical applications, and cross-comparisons.
1. SPI Surface Finish Standard
SPI divides finishes into four major categories—A, B, C, D—with a total of 12 grades, ranging from mirror polish to very rough blasted surfaces.
| SPI Grade | Processing Method | Appearance | Ra Roughness (μm) | Typical Applications | Mold Cost Level |
|---|---|---|---|---|---|
| A-1 | #3 Diamond Paste (6000#) | Super High-Gloss Mirror | 0.012–0.025 | Optical lenses, cosmetic cases, transparent parts | ★★★★★ |
| A-2 | #6 Diamond Paste (3000#) | High-Gloss Mirror | 0.025–0.05 | Phone back covers, automotive bright interior parts | ★★★★☆ |
| A-3 | #15 Diamond Paste (1200#) | Normal Gloss | 0.05–0.10 | General high-gloss appearance parts | ★★★★ |
| B-1 | 600# Wet Sandpaper | Fine Semi-Gloss | 0.05–0.10 | Appliance panels, mouse shells | ★★★ |
| B-2 | 400# Wet Sandpaper | Medium Semi-Gloss | 0.10–0.15 | Common consumer electronics housings | ★★★ |
| B-3 | 320# Wet Sandpaper | Slight Matte Semi-Gloss | 0.28–0.35 | Surfaces needing mild diffuse reflection | ★★☆ |
| C-1 | 600# Stone | Fine Matte | 0.35–0.4 | Non-cosmetic functional surfaces, internal parts | ★★ |
| C-2 | 400# Stone | Medium Matte | ≈0.6–0.8 | Engineering parts, hidden surfaces | ★★ |
| C-3 | 320# Stone | Coarse Matte | ≈1.0–1.5 | Rough functional surfaces | ★☆ |
| D-1 | Fine Glass Bead Blasting | Fine Sand/Satin | ≈0.8–1.6 | Fingerprint-resistant, non-slip grips | ★☆ |
| D-2 | Medium Aluminum Oxide Blasting | Medium-Coarse Sand | ≈3–6 | Strong anti-slip industrial handles | ★ |
| D-3 | Coarse Aluminum Oxide Blasting | Very Rough Sand | ≈10–18 | Extremely high-grip parts, outdoor equipment | ★ |
One-sentence summary for SPI: A grades →pursue ultimate glossy appearance B grades →most common semi-gloss balance point) C/D grades →functional matte/anti-slip
2. VDI 3400 Standard (Most Common for Matte/EDM Textures)
VDI 3400 is currently the most widely used matte standard in Asian and European factories, especially suited for EDM (electrical discharge machining). The official standard has 45 grades, but in practice, the 12 most common ones are VDI 12–45.
| VDI Value | Typical Processing Method | Ra (μm) Approx. | Appearance | Common Applications | Rough SPI Equivalent |
|---|---|---|---|---|---|
| VDI 12 | 600# Stone | 0.40 | Very Fine Matte | Low-requirement semi-gloss surfaces | ≈ C1 |
| VDI 15 | 400# Stone | 0.56 | Fine Matte | Common internal parts | ≈ C2 |
| VDI 18 | Coarse Glass Bead Blasting | 0.80 | Standard Fine Sand | Mice, remote controls common matte | ≈ D1 |
| VDI 21 | #240 Aluminum Oxide Blasting | 1.12 | Medium Sand | Appliances, tool housings | — |
| VDI 24 | #240 Aluminum Oxide Blasting | 1.6 | Noticeable Sand | Mid-range automotive interior matte | — |
| VDI 27 | #240 Aluminum Oxide Blasting | 2.24 | Standard Medium-Coarse Sand | Automotive interiors, power tools most common | — |
| VDI 30 | #24 Aluminum Oxide Blasting | 3.15 | Coarse Sand | Areas needing strong grip | ≈ D2 |
| VDI 33 | Coarser Aluminum Oxide | ≈4.5 | Very Coarse Sand | Outdoor equipment, bag handles | — |
| VDI 36 | Coarse Blasting | ≈6.3 | Very Rough | Industrial-grade anti-slip | — |
| VDI 39 | Extremely Coarse Blasting | ≈9 | Strong Grain Feel | Extremely special anti-slip needs | ≈ D3 |
| VDI 42 | — | ≈12.5 | Ultra-Coarse | Very rare applications | — |
| VDI 45 | — | ≈18 | Roughest | Extremely strong functional rough surfaces | — |
Lower numbers = finer/smoother; higher numbers = rougher. VDI 18–27 is the highest-usage range for consumer electronics and automotive interiors.
3. Mold-Tech (MT) Texture Standard
Mold-Tech is a U.S.-based company offering a standardized library of chemical-etched textures, with hundreds to thousands of patterns—not just roughness, but also leather, wood grain, stone, geometric designs, etc.
The most commonly used are the MT-1xxxx series (fine to medium-coarse matte).
| Series | Texture Depth (inch) | Appearance Style | Recommended Min. Draft Angle | Typical Applications |
|---|---|---|---|---|
| MT-11000 series | 0.0004–0.001 | Extremely Fine Sand/Velvet | 1°–1.5° | High-end consumer electronics, medical |
| MT-11010 | 0.001 | Fine Sand (most common) | 1.5° | Phones, laptops, cosmetics |
| MT-11020–11100 | 0.0015–0.002 | Medium-Fine Sand | 2–3° | Appliances, automotive interiors |
| Higher MT-11xxx | 0.0025–0.004 | Medium-Coarse to Coarse Sand | 4–6° | Tools, outdoor products |
| MT-30000 series | Medium to Coarse | Deeper Grain | 5–8° | Automotive exteriors, power tools |
| MT-60000 series | Very Deep | Strong Natural Textures | 8°+ | Off-road gear, furniture |
Mold-Tech Characteristics:
- Extremely rich pattern variety (leather, carbon fiber, orange peel, alligator, etc.)
- Usually requires sending the mold to a professional etching company
- Higher draft angle requirements than VDI/SPI (deeper texture needs larger draft)
| Requirement | Recommended Standard | Recommended Grade Range | Cost | Draft Requirement | Remarks |
|---|---|---|---|---|---|
| Mirror/High Gloss | SPI | A1–A2 | High | Very Low | Most expensive, brightest |
| Semi-Gloss/Fine Matte | SPI / VDI | B1–B2 / VDI 12–18 | Medium | Low | Most common balanced choice |
| Standard Consumer Electronics Matte | VDI | 18–27 | Medium-Low | Medium | Most familiar to Asian factories |
| High-End Commercial Textures | Mold-Tech | MT-11010～MT-11xxx | Medium-High | Medium-High | Widest pattern selection |
| Strong Anti-Slip/Functional Rough | VDI / SPI D | VDI 30+ / D2–D3 | Low | High | Lowest cost, function-first |
When selecting a surface texture, first clarify whether appearance or function is the priority, then consider the material (PC, ABS, glass-filled PA require larger draft), ejection difficulty, and budget. Most consumer electronics products ultimately fall into VDI 24–27 or SPI B2 + fine MT texture ranges.