Moiré is the wavy interference pattern that ruins textile prints in ways paper proofs often miss. It shows up as diagonal bands, ghostly ripples, or regular beat patterns that only become visible at bolt scale on real fabric. The causes are mathematical — three overlapping grids (file resolution, halftone screens, fabric weave) interfering with each other. The prevention is discipline at file setup and process selection.
The Three Grids That Cause Moiré
Every textile print has at least three repeating grids:
- The file pixel grid: the resolution of your digital artwork (e.g., 300 DPI)
- The halftone screen: the dot pattern the RIP creates to reproduce tones (e.g., 120 LPI)
- The fabric weave: the regular thread structure of the substrate (varies by material)
When two or more of these grids interact at the wrong relative angle or frequency, the human eye perceives a low-frequency beat pattern — moiré. The interference is real physics, not a rendering mistake.
Moiré Between File Resolution and Halftone
The most common textile moiré appears between file pixels and halftone dots. If your file resolution is too close to the halftone line ruling, the two grids beat against each other.
Prevention: file resolution should be 3× the halftone LPI:
- 40 LPI (coarse) → 120 DPI minimum, 150 DPI comfortable
- 65 LPI → 195 DPI minimum, 200 DPI common
- 120 LPI (fine) → 360 DPI minimum, 400 DPI for critical work
- 150+ LPI (very fine) → 450 DPI
Submitting 300 DPI to a 120 LPI rotary works in most cases (2.5× ratio) but shows mild moiré in gradient-heavy areas. The 3× rule exists to eliminate this risk.
Moiré Between Color Screens (CMYK Rosette)
Multi-color halftone printing layers screens for each color. If two screens share the same angle, their dots align and form visible stripes — catastrophic moiré. If they share a related angle (like 90° apart), the overlap forms a regular checkerboard pattern.
The industry-standard CMYK angles:
- Cyan: 15°
- Magenta: 75°
- Yellow: 0°
- Black: 45°
These angles are chosen because their 15° minimum separations produce a small regular "rosette" pattern that reads as smooth color at normal viewing distance. Any deviation — a Yellow screen rotated to 30°, for example — creates dramatic moiré.
For spot color work with 2–3 colors, use 45° and 75° as the dominant angles. Never place two screens at the same angle.
Moiré Between Halftone and Fabric Weave
Tight-weave fabrics have their own regular grid:
- Cotton percale: 200+ threads per inch
- Silk habotai: 120–180 TPI
- Fine polyester shirting: 150+ TPI
- Chiffon: 80–120 TPI
When a fine halftone screen (120 LPI) prints on a 180 TPI silk, the two grids interfere. The moiré may be invisible on a paper proof but appear clearly on the fabric. Loose-weave fabrics (jersey, canvas, denim) have less regular thread patterns and rarely cause this problem.
Prevention for fine-weave fabrics:
- Drop halftone LPI — use 65–85 LPI instead of 120
- Switch to flat-tone separations if the design permits
- Use spot color rather than halftone for solid fills
- Always strike off on the actual fabric before full production
How to Inspect for Moiré Before Production
- Check digital proof at 100% output size — file-to-halftone moiré shows here
- Check angled proof printouts — screen-to-screen moiré shows in the multi-color regions
- Request a physical strike-off on the production fabric — this is the only way to catch fabric-weave moiré
- Inspect strike-off from multiple angles and distances — moiré often only visible at specific viewing geometries
Skipping the physical strike-off is how moiré reaches production and becomes a reprint.
Post-File Fixes (Limited)
If moiré appears in a file already submitted, partial fixes include:
- Gaussian blur at 0.5–1.5px: softens high-frequency detail feeding interference. Costs overall sharpness.
- Resample to a different resolution: breaks beat frequency with halftone. Changes file size and detail.
- Convert halftone regions to spot color: bypasses halftone screening entirely. Requires redesign.
None of these are clean fixes. Prevention at file setup is always cheaper than post-file correction.
Moiré Prevention Checklist
- ✓ File resolution ≥ 3× halftone LPI
- ✓ CMYK screens at 15° / 75° / 0° / 45° (never overlap)
- ✓ Halftone LPI appropriate for fabric weave (lower for fine weaves)
- ✓ No fine line patterns or textures at frequencies near halftone ruling
- ✓ Strike-off on actual production fabric before full run
- ✓ Inspection from multiple angles and distances
Related Reading
For the DPI side of the equation: DPI for fabric printing. For color separation decisions that affect halftone use: color separation guide. For the complete artwork prep framework: textile artwork preparation guide.
