Plastic Part Surface Finishes: Texture, Paint, Print & Laser

A molded part is not finished until its surface is decided. Gloss level, grain, colour and graphics can all be produced by more than one route, and each route carries a different tooling cost, a different per-part cost and a different durability claim. Deciding a finish after the tool is cut is the most expensive way to choose it.

Surface finishes split into two families. Finishes built into the tool — mold texture, molded-in colour and gloss level — are paid for once in tooling time and then cost nothing per part. Finishes applied after molding — painting, printing, laser marking and plating — add a per-part cost and a second process step, and they can usually be added later if volumes justify it.

Xiamen Yistar Precision Manufacturing Co., Ltd, established in Xiamen in 1995, reviews texture, print and finish requirements during the DFM stage, before the cavity is cut. That sequencing matters because grain depth and draft angle are decided together, and a texture specified after the tool is finished means welding, re-polishing and re-texturing.

Key Takeaways

• Mold texture is specified either as an SPI grade or as a VDI 3400 number, and the controlling value is not the name of the grain but its depth in micrometres.
• A light matte finish runs roughly 12 µm to 25 µm deep and a heavy leather grain 50 µm to 100 µm, and every 0.025 mm of depth needs about 1° of extra draft per side.
• Molded-in texture, molded-in colour and gloss level add tooling time and effectively no per-part cost, which makes them the cheapest finishes at volume.
• Painting hides flow marks and weld lines but adds a per-part cost and a rework risk at every coat, while laser marking adds graphics without ink, solvent or a drying step.
• Pad printing, screen printing and laser marking all put text or logos on a molded part, but only laser marking is a single-step process that removes material instead of adding ink.

What Surface Finishes Can Be Applied to a Molded Plastic Part?

Molded parts take two kinds of finish: finishes formed by the tool itself, such as mold texture, molded-in colour and gloss level, and finishes applied after molding, such as painting, pad printing, screen printing, laser marking and electroplating. The first is a one-time tooling decision; the second is a repeating production cost.

Molded-in texture is the most durable option because the grain is part of the surface, not a coating on top of it. Nothing can flake off, and the finish survives handling, cleaning and abrasion for the life of the part. The limits are that every texture consumes draft and that a tool can hold only one grain per surface area.

Applied finishes exist because they do something the tool cannot. Paint delivers a colour match across different materials or a metallic and soft-touch effect. Printing delivers variable data, serial numbers and multi-colour graphics. Laser marking delivers permanent, machine-readable codes at high speed.

How Do Mold Texture Grades Work?

Mold texture is graded on two scales: the SPI finish standard, which runs from A-1 high gloss to D-3 heavy matte, and the VDI 3400 standard, which numbers acid-etched grains from 12 to 45. What matters in practice is depth, because depth is what the part must release from.

Depth drives draft. A texture that is 1 µm deep needs almost no extra release angle, while a 100 µm grain can push the requirement from 1° to 3° per side or more. The reason is mechanical interference: the texture interlocks with the steel at the parting surface, and the steeper the wall, the less force is needed to break that interlock.

Depth also drives cosmetic risk. A deep grain hides flow marks, weld lines and minor sink because light scatters across the texture, which is why a heavily textured part is often easier to qualify than a gloss one. Gloss is the least forgiving finish on the same tool, because any surface disturbance shows as a visible optical distortion.

Should You Choose Molded-In Texture or Paint?

Choose molded-in texture when the part must keep its appearance without a second process, and choose paint when the colour cannot be molded, the effect requires a coating, or the parts come from several materials that must match. Molded-in texture is more durable; paint is more flexible.

Molded-in colour is the cheaper option at volume because it removes a process step and its associated handling, drying and rework. It also removes an entire inspection problem: there is no film thickness to control and no adhesion test to pass. The trade-off is a minimum order quantity on coloured resin and a narrower palette than paint can offer.

Painting makes sense where a colour match must be held across different materials and processes, where a metallic or soft-touch effect is required, or where the part is still changing. Painting also repairs a cosmetically marginal moulding, since a coat of paint covers flow marks that a gloss tool would expose. The costs are real: masking, primer, topcoat, oven time and a reject rate that rises with every coat.

Our guide to mold design fundamentals: draft angles, gates, runners and cooling explains how texture depth and draft interact in the tool, and our guide to selecting a plastic electronic enclosure case kit shows how finish choices are made for enclosure programmes.

Can You Print on an Injection Molded Part?

Yes. Pad printing, screen printing, hot stamping and laser marking are all used on molded parts, and the choice depends on the surface geometry, the ink system and how permanent the graphic must be. Flat surfaces take screen printing, curved and recessed surfaces take pad printing, and variable data takes laser marking.

Pad printing transfers ink from a silicone pad, so it reaches curved, stepped and slightly recessed areas that a screen cannot cover. It is fast and inexpensive per print, and it handles multiple colours with multiple passes. Its limits are that the ink sits on the surface and can wear, and that each colour needs its own plate and its own pass.

Screen printing lays a thicker ink film through a stencil and gives a more opaque, more saturated print, which makes it a good fit for large flat panels and high-contrast graphics. It is less suited to compound curves and to small parts with fine detail, where pad printing has the advantage.

In-mold labelling is the third route: the graphic is printed on a film insert that is placed in the cavity and bonded to the part during molding. The label cannot peel or rub off because it is encapsulated, and the process suits high-volume panels where the added cycle time is offset by the elimination of a separate printing step.

How Does Laser Marking Compare with Pad Printing?

Laser marking burns or foams the surface layer of the part with a focused beam, so the graphic is part of the material and cannot wear off. Pad printing applies ink on top of the surface, which gives more colour options and a softer capital cost. The right choice depends on permanence, colour and volume.

Laser marking needs a resin that absorbs the laser wavelength, so light and natural-coloured grades mark better than dark or heavily loaded ones; additives and masterbatches can be used to improve contrast. It costs nothing per print apart from machine time, but the equipment is capital intensive, so it usually sits with the molder rather than the customer.

Pad printing's advantage is colour. A white logo on a dark housing, a two-colour badge or a metallic ink is straightforward on a pad printer and difficult or impossible with a laser. Where the marking must survive solvents, abrasion or outdoor exposure, laser marking or an encapsulated in-mold label is the safer specification.

What Does Each Finish Change About Cost and Lead Time?

Every finish trades cost between tooling and production. Molded-in texture and colour sit entirely in tooling and material, so they add days to the tool build and nothing to the piece price. Painting, printing and plating sit entirely in production, so they add cost and a process step to every part.

Mold texture adds tooling time for etching, photography and inspection, and it must be agreed before the cavity is finished. Painting adds primer, topcoat, curing and inspection, and it introduces a reject rate that rises with the number of coats. Laser marking adds machine time only and no consumable, which makes it the cheapest of the applied finishes per part in high volume. The molding cycle that carries those parts, including the ejection forces a deep texture has to survive, is described step by step in our guide to the injection molding process. Where a finish adds a production step, its cost lands in the piece price alongside material and machine time, which is the split our cost breakdown for an injection molded part sets out.

The comparison below ranks each finish by where its cost lands rather than by an absolute price, because the absolute figure scales with part surface area and batch size.

For Custom Engineering Plastic Components, the finish decision is made against the same 3D data as the draft and gate review, so the texture depth, the draft angle and the ejection layout are agreed as one specification. That review is described in our playbook for sourcing custom injection molding from China.

FAQ

What is the difference between SPI and VDI texture standards?

SPI grades finish quality from A-1 high gloss to D-3 heavy matte, based on surface roughness rather than a specific pattern. VDI 3400 numbers acid-etched grains from 12 to 45 by increasing etch depth. Both are used on drawings, but SPI describes appearance while VDI describes the pattern and its depth.

Can you paint an injection molded part?

Yes, and painting is routine on cosmetic housings. The part is cleaned, primed, topcoated and cured, usually with masking on the areas that must stay conductive or bondable. Painting hides flow marks and weld lines, allows a colour match across different materials, and adds a per-part cost plus a reject rate.

How deep can a mold texture be before draft becomes a problem?

Textures deeper than about 50 µm normally need 2° to 3° of draft per side, and grains of 100 µm can require 3° to 5°. The working rule is roughly 1° of additional draft for every 0.025 mm of texture depth. Shallow grains under 25 µm usually run on standard draft.

Does laser marking work on any plastic?

No. Laser marking needs a resin that absorbs the laser wavelength, so light and natural grades mark with better contrast than dark or heavily filled ones. Additives and masterbatches can be specified to improve contrast, and some resins foam rather than carbonise, which gives a lighter mark on a dark part.

Conclusion

Surface finish is a specification, not an afterthought. Mold texture depth decides draft angle, draft angle decides ejection, and the finish applied after molding decides both the per-part cost and the durability claim you can make to a customer.

The cheapest durable finish is almost always the one built into the tool, provided the colour can be molded and the texture is agreed before the cavity is cut. Where a colour match, a metallic effect, variable data or a permanent machine-readable code is required, an applied finish earns its cost, and it can be added at any time.

Send us the part and the appearance you need. Xiamen Yistar Precision Manufacturing Co., Ltd will specify texture, draft and finish together before the tool is cut, and quote the molding with any applied finish that the design requires.

Contact Us

Xiamen Yistar Precision Manufacturing Co., Ltd
Address: Room 401, No. 37 Huliyuan, Tong'an District, Xiamen, Fujian, China
Phone / WhatsApp: +86-18064076912
Email: info@yistar-plastic.com
Open Hours: 24 Hours