Texture and Graining: What It Hides, What It Makes Worse, and What It Costs

“The grain will cover it” is one of the most frequently used sentences in a mold trial review, and one of the least examined. Texture does hide a great deal — that is why so many consumer and automotive parts are grained rather than glossy. But the list of what it hides is finite, the list of what it makes worse is short and specific, and the draft it demands is larger than most people expect.

This guide covers all three. It sits alongside mold surface finish, which explains how finish is specified with SPI and VDI grades; this page is about what that specification buys you and what it does not.

What Texture Genuinely Hides

Eastman’s mold design guidelines put the list plainly. Texturing is useful for hiding weld lines, flow marks, gate blush, sink marks, and scuffing.

That is a large fraction of the entire cosmetic defect list, and it explains a decision buyers sometimes read as a cop-out: choosing a grained surface over a gloss one is not an admission that the part will be imperfect. It is buying tolerance for the defects that molding produces anyway.

Two refinements from the same source are worth knowing, because they are the levers a supplier has when a grain is not quite doing its job:

• For a higher-matte result, the etching can be doubled or tripled.
• A rounded texture pattern hides a visible weld line better than a sharp-edged one — and is also the better choice on a resin with poor scratch resistance, because it disguises marks the part will pick up in service.

That second point is worth raising early on a part that will be handled. Scratch visibility is a texture-pattern decision, and it is much cheaper to make before the pattern is etched than after.

What Texture Makes Worse

This is the shorter list and the more expensive one. Three defects survive graining, and one of them is created by it.

Anything with height. Texture is a surface relief measured in hundredths of a millimetre. It cannot hide something that stands proud of the surface — a step at a parting line, or a raised secondary weld line, the ridge left where a flow front stalls and restarts. A grain follows the bump; so does paint.

Gate blush. The high-shear zone around a gate can locally wipe out the grain, leaving a smooth, shiny patch in a matte field. That is arguably worse than the original blemish, because a defect that breaks the texture pattern draws the eye more than one that merely varies the tone.

Ghosting. A shadow that appears on a grained surface, often echoing a feature on the back face. It exists only after texturing, which means it is discovered at the last possible moment — after the tool has been sent out, etched, and returned.

The pattern across all three is the same: texture varies how light scatters; it does not change the geometry underneath. Defects that are tonal get masked. Defects that are dimensional do not.

One more that is not the texture’s fault

Uneven gloss within a single grained surface reads as a texturing defect and usually is not.

Eastman’s guidance is explicit that uniform mold temperature is needed for the texture to come out even across the pattern, and that abrupt changes in wall thickness, relatively thick sections, and heavy ribs cause variations in surface gloss. So a part with visible tonal banding inside one grain may be telling you about its cooling or its wall thickness, not about the etch.

Worth checking before the texture is blamed and re-etched at cost.

The Draft Bill

Texture grips steel. That is the whole mechanism, and it has a published conversion.

Eastman’s guidelines give 1° to 1.5° of additional draft for every 0.025 mm (0.001 in) of texture depth, against a typical texture depth of 0.06–0.08 mm (0.0025–0.0030 in).

Work that through:

Texture depth	Additional draft required
0.001 in (0.025 mm)	1° – 1.5°
0.0025 in (0.06 mm) — typical light grain	~2.5° – 3.75°
0.0030 in (0.08 mm) — typical deeper grain	~3° – 4.5°

That is on top of whatever the face needed to release when it was smooth — where the same source suggests around 1° per side as a general starting point.

So a wall drawn vertical for styling reasons, then grained, may need four or five degrees of taper it does not have. This is why a late texture decision so often reopens the part design rather than just the tooling quote, and why the same guidance says to settle the pattern early so draft and contours can be designed around it.

The failure mode when it is not settled early is drag: the part scrapes the pattern on the way out, and you get scuffing, stress whitening, or in bad cases texture that tears off the steel. See draft angle.

How Texture Is Applied, and Why It Matters to the Schedule

Four methods appear in the published guidance, and they are not interchangeable:

Method	Notes
Photoetching	Described as the most common texturing procedure
EDM / spark erosion	Makes economic sense when the cavity is being EDM’d anyway
Sandblasting	Suitable only for mostly flat surfaces
Matte chromium plating	Produces a matte, wear-resistant texture
Mold polishing	Gloss level controlled by varying the polishing grit

Photoetching usually means the tool — or the cavity insert — leaves the mold shop and goes to a texturing house. That is a shipping-and-queue step in the middle of your tooling schedule, and it is the practical reason “we’ll decide the grain later” costs weeks rather than days.

It is also close to irreversible. Deepening a texture is possible; removing one means polishing the cavity back and re-etching, which changes dimensions. Which is why reviewing a smooth, pre-texture sample before the tool is grained is one of the cheapest requests in a tooling program: it costs a shipment and a week, and it is the only look you will get at the defects the grain is about to hide. See T1 and T2 trials.

The Counterintuitive Part: Polish Is Not the Safe Choice

The instinct on a cosmetic part is to specify the finest finish available. Published guidance pushes back twice.

Eastman states that surfaces polished smoother than required for ejection only add to mold cost, and that highly polished surfaces can hinder ejection where a vacuum is drawn in low- or no-draft areas. Their suggested countermeasure is a light 320 dry grit blast — an SPI B-3 finish — on drafted walls, specifically to stop a vacuum forming.

BASF makes the same point from the material side for soft TPU: polished and chrome-plated mold surfaces are called out as less suitable because soft grades stick to them, with a matte surface around Rz 25–35 µm recommended for release instead.

So when a supplier proposes a light blast on a face you wanted glossy, it may not be a compromise on appearance. It may be the thing keeping your part from sticking in the tool.

Buyer FAQs

Does texture hide molding defects?

Some of them. Published guidance lists weld lines, flow marks, gate blush, sink marks and scuffing as defects texturing is useful for hiding. It does not hide anything with physical height — a step at a parting line or a raised secondary weld line stands proud of the surface and the grain follows it. Gate blush can also locally destroy the texture, producing a shiny patch that is more visible than the original mark.

How much extra draft does a textured surface need?

One published conversion gives 1° to 1.5° of additional draft for every 0.001 in (0.025 mm) of texture depth, against typical texture depths of 0.0025–0.0030 in. That works out to roughly 2.5° to 4.5° added to whatever the smooth face already required. Because the requirement is that large, the texture pattern should be settled before faces are drawn, not after.

Why does one grained surface look different in different places?

Often it is not the texture. Uniform mold temperature is needed for a grain to come out evenly, and abrupt wall thickness changes, thick sections, and heavy ribs produce gloss variation within the same pattern. Tonal banding inside a single grained face is worth investigating as a cooling or wall thickness issue before the etch is blamed.

Can a texture be changed after the tool is made?

Deepening a texture or going to a higher matte is generally possible — the etching can be repeated. Removing or lightening one means polishing the cavity back and re-texturing, which removes steel and changes dimensions. Treat the pattern as close to permanent, and review a smooth pre-texture sample before the tool is grained.

Is a high-polish finish safer than a texture for a cosmetic part?

Not necessarily. A gloss surface reveals sink, flow lines and weld lines that a grain would mask, so it raises the bar on the rest of the design and process. Published guidance also notes that polishing beyond what ejection requires only adds mold cost, and that a highly polished surface can hinder ejection where a vacuum forms in low-draft areas — which is why a light blast is sometimes added deliberately.

How This Guide Was Put Together

Texture depth, the draft conversion, the list of defects texturing hides, the texturing methods, and the uniform mold temperature requirement are taken from one resin manufacturer’s published mold design guidelines and are quoted as printed there. Surface roughness guidance for soft elastomers comes from a second manufacturer’s processing recommendations. Texture depths, patterns and the draft they require vary by grain, resin, and supplier; the figures here indicate scale and relationship rather than a specification for any particular part.

Disclaimer

PlasticsTechnologyAlliance.com is an independent buyer resource. It does not manufacture parts, texture tooling, or certify suppliers. Texture selection and the draft it requires should be agreed with your supplier and the texturing house before mold design is frozen.