Technical reference
Mold Texturing Guide
The independent technical reference for surface texturing in plastic injection molding. We document the standards engineers actually specify on drawings, VDI 3400, SPI surface finish and Mold-Tech, together with the draft angle and surface roughness rules that decide whether a textured part releases cleanly from the tool.
What is mold texturing?
Mold texturing is the controlled surface finish applied to the cavity of an injection mold, which every molded part copies exactly. It sets how the part looks and feels, from a mirror polish to a deep leather grain, and it changes how much draft the part needs to eject without scuffing. Texture is specified on the drawing with a standard grade or a pattern code, then produced in the tool steel by polishing, EDM, chemical etching, laser ablation or abrasive blasting.
- What it controls: gloss and appearance, grip, scratch and fingerprint resistance, and the hiding of flow lines, sink and weld lines.
- How it is specified: SPI grades for polished and blasted finishes, VDI 3400 grades for EDM roughness, and Mold-Tech pattern codes for decorative grains.
- Why it matters in tooling: texture depth drives draft angle, and a texture specified without enough draft drags on ejection and damages both the part and the tool.
The three texture systems at a glance
SPI, VDI 3400 and Mold-Tech describe different things, which is why a callout in one system rarely converts cleanly into another.
| System | Origin | What it defines | Scale | Roughness range | Typical use |
|---|---|---|---|---|---|
| SPI surface finish | United States, Plastics Industry Association (formerly SPI) | Finishing method and visual result | 12 grades, A-1 to D-3, in four families: glossy, semi-gloss, matte, textured | About 0.025 µm or less (A-1) to 5.8 µm (D-3), DME reference values | Polished, semi-gloss, stoned and blasted cavities |
| VDI 3400 | Germany, Association of German Engineers (VDI) | Surface roughness of EDM textures | 12 reference grades, VDI 12 to VDI 45, logarithmic | Ra 0.40 µm (VDI 12) to 18.00 µm (VDI 45) | Uniform matte EDM textures in global tooling |
| Mold-Tech | Standex Engraving, proprietary | Texture pattern: grain, leather, wood, geometric | Pattern library identified by codes such as MT-11000 | No roughness scale; specified by pattern and depth | Automotive interiors and decorative consumer parts |
Values are approximate and summarize the detailed pages linked below; SPI roughness follows the DME mold finish guide. Confirm every finish against a physical reference sample before tool release.
Key rules engineers check first
- VDI 3400 is logarithmic: every 6-step rise in the VDI number roughly doubles Ra, so VDI 24 is about twice as rough as VDI 18. See the VDI 3400 chart.
- SPI A has no VDI equivalent: the glossy A grades are smoother than the finest VDI reference grade, so a mirror callout cannot be expressed as a VDI number. See SPI A glossy finishes.
- Draft follows depth: add roughly 1.0 to 1.5 degrees of draft for every 0.001 inch (0.025 mm) of texture depth, on top of the base draft the geometry already needs. See draft angle by texture.
- Mold-Tech does not convert officially: it is a pattern library, not a roughness scale, so any SPI or VDI equivalent is an approximation to confirm with the texturing supplier. See the conversion chart.
Texture standards and specifications
The systems specified across global tooling supply chains, with how they are measured, where they diverge and how to convert between them.
VDI 3400 surface finish
The German EDM roughness standard: all 12 reference grades with Ra in µm and µin, the VDI to Ra formula and draft guidance per grade.
Read the standard →SPI surface finish
The North American system of 12 grades from A-1 to D-3. Why SPI is a method and an appearance, not only an Ra number, plus steel and polymer effects.
Read the standard →SPI A glossy finish
The diamond-buffed grades A-1, A-2 and A-3: their Ra ranges, the high-chrome steel and amorphous polymers they need, and the defects gloss exposes.
Read the guide →SPI D textured finish
The dry-blasted grades D-1, D-2 and D-3: glass bead versus aluminum oxide, DME roughness values, draft by grade and how the finish wears in production.
Read the guide →EDM surface finish
How spark erosion creates the random, non-directional matte surface that VDI 3400 grades, and how roughness is controlled in the machine.
Read the guide →Mold-Tech textures
The proprietary Standex pattern library, how MT patterns are specified on a drawing, and the texture depth rule that drives draft angle.
Read the guide →Conversion chart
Every SPI grade with its Ra range and approximate VDI 3400 position, plus where Mold-Tech fits and where a direct conversion does not hold.
Open the chart →Texturing processes
How the texture is physically created in the tool steel, and what each process means for depth, repeatability and draft.
Chemical etching
How acid etching through a photo mask forms leather, wood and decorative patterns, how etch depth is controlled, and the draft each depth requires.
Read the guide →Laser texturing
How a pulsed laser ablates a digital texture file layer by layer, wrapping patterns around complex 3D cavities with the highest repeatability.
Read the guide →Sandblasting
Abrasive blasting with glass bead and aluminum oxide: the SPI D finishes it produces and how a final blast sets the gloss of other textures.
Read the guide →EDM texturing
Electrical discharge texturing in practice: electrodes, dielectric, roughness control and when to choose EDM over etching or laser.
Read the guide →How to choose a texture specification
A short sequence that prevents the most common and most expensive texture mistakes.
- Start from the part's function. Optical and transparent parts need SPI A polish; cosmetic covers usually take SPI B or a fine VDI grade; grip surfaces and parts that must hide molding marks take a coarser VDI grade, an SPI D blast or a Mold-Tech pattern.
- Use the system your supply chain reads. SPI is common for polished finishes in North America, VDI 3400 for EDM matte finishes worldwide, and Mold-Tech codes for patterned grains, especially in automotive.
- Check draft against texture depth. Confirm the walls carry enough draft for the chosen depth before the tool is cut, because adding draft later means modifying the steel.
- Match steel and polymer to the finish. High gloss needs a high-chrome steel and an amorphous resin; filled and semi-crystalline resins dull a polished cavity and change how a texture reads.
- Approve a physical sample. Sign off the finish on a reference plaque or a first-shot part in the production resin, since two surfaces with the same Ra can look different.
Texture and design
How texture choice changes what a part designer has to allow for, starting with the rule that costs the most money when it is missed.
Draft angle by texture
How much draft each texture depth demands, why deeper textures need more, and the degrees-per-finish reference for clean release.
Read the guide →Reference
Need a quick definition? The glossary covers the core terms used across mold texturing, from Ra and EDM finish to shrink-away and orange peel.