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

“The grain will cover it” shows up constantly in mold trial reviews, and it is rarely examined. Texture does hide a lot; that is why so many consumer and automotive parts are grained instead of glossy. What it hides is finite. What it makes worse is short and specific. The draft it demands is larger than most people expect.

It sits next to mold surface finish, which covers how finish is specified with SPI and VDI grades. Here the question is 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 covers a large share of cosmetic defects, and it reframes a decision buyers sometimes read as a cop-out: choosing grain over gloss is not admitting the part will be imperfect. It is buying tolerance for defects molding produces anyway.

Two refinements from the same source matter 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 it is also better on a resin with poor scratch resistance because it disguises marks the part will pick up in service.

Raise that second point early on a handled part. Scratch visibility is a texture-pattern decision, and it is much cheaper before the pattern is etched than after.

What Texture Makes Worse

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

Anything with height. Texture is surface relief measured in hundredths of a millimetre. It cannot hide something that stands proud of the surface: a parting-line step, or a raised secondary weld line 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 can look worse than the original blemish, because a break in the texture pattern draws the eye more than a tone variation.

Ghosting. A shadow on a grained surface, often echoing a feature on the back face. It appears only after texturing, so it is discovered late: after the tool has been sent out, etched, and returned.

The pattern is the same across all three: texture changes how light scatters; it does not change the geometry underneath. Tonal defects get masked. Dimensional defects do not.

One more that is not the texture’s fault

Uneven gloss inside one grained surface reads as a texturing defect and usually is not.

Eastman is explicit that uniform mold temperature is needed for even texture across the pattern, and that abrupt wall-thickness changes, relatively thick sections, and heavy ribs cause gloss variation. Tonal banding inside one grain may be telling you about cooling or wall thickness, not the etch.

Check that before you blame the texture and re-etch at cost.

The Draft Bill

Texture grips steel. That is the 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 smooth. The same source suggests around 1° per side as a general starting point for a smooth face.

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

When draft is missing, the failure mode is drag: the part scrapes the pattern on the way out. 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 for a texturing house. That is a shipping-and-queue step in the middle of your tooling schedule, and it is why “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. 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 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 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 what keeps the 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. It does not hide anything with physical height (parting-line step, raised secondary weld). Gate blush can also wipe the texture locally into a shiny patch that is more visible than the original mark. Before you accept “grain will cover it” as closure on a T1 finding, classify the defect as tonal or dimensional.

How much extra draft does a textured surface need?

One published conversion: 1° to 1.5° of additional draft per 0.001 in (0.025 mm) of texture depth, against typical depths of 0.0025–0.0030 in. That is roughly 2.5° to 4.5° on top of the smooth-face draft. Settle the pattern before faces are drawn. If texture is chosen after CAD freeze, reopen draft before you approve the etch.

Why does one grained surface look different in different places?

Often it is not the texture. Uniform mold temperature is required for even grain, and abrupt wall changes, thick sections, and heavy ribs produce gloss variation inside the same pattern. Investigate cooling or wall thickness before you authorize a re-etch.

Can a texture be changed after the tool is made?

Deepening or going higher-matte is generally possible by repeating the etch. Removing or lightening means polishing the cavity back and re-texturing, which removes steel and changes dimensions. Treat the pattern as near-permanent, and require 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. Gloss reveals sink, flow lines, and weld lines that grain would mask, so it raises the bar on design and process. Published guidance also notes that polishing past what ejection needs only adds mold cost, and that high polish can hinder ejection where vacuum forms in low-draft areas. That is why a light blast is sometimes added on purpose.

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.