VDI 3400 is the German engineering standard for molded plastic textures, and it describes what the surface looks and feels like rather than how smooth it measures. SPI surface finish answers a roughness question in micrometers; VDI 3400 answers an appearance question with a numbered texture code. Most confusion between the two comes from expecting one to do the other’s job.
Key takeaways
- SPI and VDI 3400 are not alternatives. SPI (Ra in µm) governs smoothness and gloss. VDI 3400 governs the visible texture structure. A part can be SPI A-1 smooth and still carry a coarse VDI texture.
- VDI textures are machined, not coated. They are cut into the cavity surface with fine-grain EDM electrodes, which is why they cost more than polishing and cannot be polished off.
- Every cavity is machined separately. A 4-cavity textured tool is four textures, four times the cost, and four times the opportunity for variation.
- Texture forces design changes. Mold steel must be thicker under the cavity face, draft must increase, and ejection needs more area.
- Specify the VDI code, not an adjective. “Fine matte” is not a specification. VDI 2702 is.
SPI and VDI 3400 answer different questions
These two systems are routinely confused, and mixing them produces quotes nobody can compare.
SPI finish grades run from A-1 (high-gloss diamond polish, most expensive) to D-3 (as-machined, least expensive). They are measured in Ra micrometers and describe how smooth the surface is. A mirror finish can add $1,000–$3,000 per cavity. This is the reference point for gloss, sealability and cleanability.
VDI 3400 is a texture standard. It assigns each texture a number based on its visual and tactile structure — fine matte, coarse grained, leather-like, technical. It says nothing about Ra. A VDI 2702 surface and an SPI A-1 surface are not the same thing, and neither is better; they solve different requirements.
Our injection mold surface finish guide covers the SPI system in full. This guide is about the other half.
The VDI 3400 codes you will actually see
VDI codes are written as a base number plus a structure number. In practice four families cover most molded plastic parts.
| VDI 3400 code | Appearance | Typical use |
|---|---|---|
| 2402 | Very fine, even matte | Medical housings, laboratory equipment, visible consumer parts |
| 2502 | Fine matte / fine sandblast look | Appliance fascias, cosmetic enclosures, kitchen products |
| 2602 | Medium matte, clearly visible structure | Automotive interior trim, luggage, tool handles |
| 2702 | Coarse matte, pronounced grain | Grip surfaces, sports equipment, industrial housings |
Beyond those there are leather-grain, technical-structure and decorative families. The important commercial point is that the buyer specifies the code, not the mood. Our materials guide covers how resin choice interacts with texture appearance, which is a factor buyers often miss.
Textures are machined, which changes the economics
A VDI texture is cut directly into the cavity steel using fine-grain EDM. This is a subtractive, electrode-based process: a fine-grain electrode is shaped to the texture pattern, then used to machine the surface. The result is a regular micro-pit structure with a defined depth, typically in the range of a few tens of microns.
Three consequences follow, and they all affect the quote:
- It is more expensive than polishing. Polishing is a finishing pass; texturing is a material-removal operation that needs a prepared electrode and a controlled setup.
- It cannot be polished off. A texture is geometry, not a finish layer. If a textured tool needs rework, the pocket reverts to as-machined and the whole texture has to be re-machined.
- Each cavity is separate. There is no copying step. A four-cavity textured tool carries four times the texturing cost of a single-cavity one.
Our machining capacity matters here: we run 6 EDM machines including Sodick mirror-finish and twin-head units, and 3 wire EDMs. Fine-grain texturing on a production cavity is a specific discipline within that, and it is worth asking a supplier directly how many textured tools they have cut. The five pricing factors guide shows where texturing sits in the overall cost stack.
Texture forces three design changes
This is the part buyers are rarely told before the tool is quoted, and it is where texture projects go wrong.
- The mold needs more steel under the cavity face. A textured surface has depth. Without extra steel, the core weakens and the cavity face distorts under clamping load.
- Draft must increase. A textured surface has undercuts at the micro level. A part designed for 1 degree draft may not release cleanly on a textured tool; 2–3 degrees is the usual working range, and the draft angle guide covers the rest of that geometry.
- Ejection needs more area. A textured surface increases the contact area between part and core, which increases ejection force. On a large textured panel this is frequently the limit that decides whether the tool releases at all.
None of these are prohibitive. They are, however, decisions that have to be made at design stage. A texture added to a tool built for a polished surface is not a finishing change; it can be a tool rebuild.
Texture and tolerances are in tension
A textured surface cannot be held to the same dimensional tolerance as a polished one, for a straightforward reason: the texture itself has a depth, and that depth is subject to variation. Specifying ±0.01 mm on a dimension measured across a textured surface is not a tighter requirement; it is an unachievable one.
Our machining tolerance is ±0.005 mm on critical mold dimensions. The molded part tolerance that tool can then hold is ±0.01 mm on critical dimensions, subject to the resin and the part geometry. On textured parts, functional dimensions away from the texture can still be held to that standard, while appearance dimensions should be specified with the texture code and an acceptance reference rather than a number. The tolerances guide covers how to structure that specification.
Resin choice changes how a texture reads
The same VDI code looks different on different materials, because gloss and texture interact with how the resin flows and how the surface scatters light.
Glossy resins such as ABS and PC show a texture more sharply because the base surface is reflective. Semi-crystalline resins such as PP and PA66 generally read slightly softer because the crystalline structure scatters light differently. The PA66 vs POM comparison covers that family in detail.
The practical rule for the buyer: approve the texture on a physical sample in your intended resin, not from a photograph. A texture that looks right in an ABS sample can look wrong in PP, and re-machining a tool to correct a texture you never physically approved is one of the most expensive mistakes in this entire process.
Where texture is used, and where it is not
Texture earns its cost where it does a job rather than where it looks decorative.
- Grip and handling — tool handles, sports equipment, consumer products where a polished surface is slippery. This is functional, and it survives scrutiny.
- Appearance consistency — a uniform texture hides minor tool marks and molding flow lines that a polished surface would show. On high-gloss visible parts, a fine texture is a legitimate defect-masking strategy.
- Cosmetic matching — matching a textured component to a textured adjacent component so the assembly reads as one visual surface.
Texture is not a substitute for good design. A part that needs texture to hide a poor parting line or an obvious flow mark has a tool problem, and the texture is making it more expensive rather than cheaper. Our injection molding design guide covers the design decisions that keep a part toolable in a polished state.
Comparing quotes that include texture
Texture quotes diverge more than any other line item, because the same phrase can mean different things to different suppliers. Before comparing, fix these four:
- The exact VDI code, not “matte” or “fine texture”.
- Whether the texture applies to the core side only, the cavity side only, or both. This is commonly the largest single difference between two quotes for what appears to be the same part.
- Whether the texture is applied to every cavity or to a subset.
- The draft angle and ejection method the supplier has assumed to make the texture releaseable.
Once those four match, the comparison is meaningful. Until then, a 40% spread between two texture quotes is normal rather than a pricing problem. Our injection molding cost guide covers the surrounding cost structure.
Texture and production volume
Texturing is a fixed cost on the tool, and like every other fixed cost it should be judged against volume. On a high-volume part the texture is amortised across hundreds of thousands of shots and is almost irrelevant to the unit price. On a low-volume part it can be a significant share of the tooling invoice, and the same money may buy more elsewhere.
That is the argument for deciding texture at the design stage rather than the quoting stage. A texture decided before quoting can be compared against all the other tool options. A texture added later can only be accepted or rejected, because by then the steel is already cut. Our first mold cost guide covers the other decisions that compete for the same budget.
Application notes from three industries
Automotive interiors are the heaviest users of VDI textures, because interior surfaces are seen at close range, handled constantly, and expected to remain presentable for years. Typical codes sit in the 2502–2702 range, with grain direction often specified to match adjacent components. Our automotive injection molding guide covers the wider automotive context.
Medical devices generally go the other way — smooth, cleanable, and specified by Ra rather than by texture, because hygiene surfaces and parting lines are the concern. The medical plastics material guide covers that decision.
Consumer electronics and appliance housings sit in between, where a fine texture on the visible face of an enclosure reduces both the appearance of flow lines and the visibility of fingerprints. Fine VDI codes in the 2402–2502 range are common here.
What to ask for with any texture quote
- The VDI 3400 code, stated explicitly and separately for each textured surface.
- A physical sample in your intended resin, approved before the tool is machined.
- The draft angle and ejection method the supplier has assumed.
- Which faces are textured and which are polished, listed face by face.
- The steel thickness under the cavity face, to confirm the texture has material to sit in.
If a supplier cannot supply the code and a sample, the quote is for an appearance, not for a specification.
Related guides in this series
- Injection mold surface finish guide — the SPI system that this one complements.
- How tight can injection molding tolerances be — why appearance dimensions and functional dimensions need different specs.
- Injection molding draft angle guide — the geometry change a texture forces.
- How to choose mold steel — because textured tools need more steel under the face.
- Injection molding materials guide — how resin choice changes how a texture reads.
Get a texture quote with a physical sample
Send the 3D file, the resin, the surfaces that need texture and the VDI codes you have in mind. We will confirm which faces can carry the texture at your draft angles, what steel thickness that requires, and what it does to the tool cost — and we will cut a sample in your intended resin so you approve the appearance rather than a photograph. Request a texture quote.