Bright, Semi-Dull, Full-Dull: Lustre Is Decided in the Polymer Plant
A polyester fabric's lustre is set not at the dyehouse but by the amount of TiO₂ delustrant blended into the polymer melt. This guide explains the three lustre classes — bright, semi-dull, full-dull — and how each changes opacity, hand, depth of shade, and UV behaviour.
Whether a fabric reads as bright or matte is locked in earlier than most buyers assume — not at dyeing or finishing, but before the yarn even exists, in the melt at the polymer plant. Lustre is governed by the proportion of titanium dioxide (TiO₂) delustrant blended into the molten PET. TiO₂ is a high-refractive-index, insoluble white pigment; its sub-micron particles, embedded in the filament body, scatter light, breaking up the fibre's glassy surface reflection and converting the specular shine the eye reads as "lustre" into a matte diffusion. This is an extension of melt-spinning physics and PET polymer chemistry, and is best read alongside our pet-polymer-iv and melt-spinning (POY/FDY) guides.
Why TiO₂ is added in the polymer, not at dyeing
TiO₂ is not a dye but an insoluble pigment; it has to be physically embedded inside the fibre matrix. It is therefore dosed into the melt as a slurry (TiO₂ dispersed in MEG) after esterification, before/during polycondensation, and becomes permanently trapped, inseparable from the fibre. Disperse dye, by contrast, diffuses into the fibre's amorphous regions at ~130 °C in the dyehouse (see the disperse-dyeing-process guide) and sets the colour — not the lustre. This yields a practical truth: lustre is a polymer/yarn choice and cannot be undone. The same dye recipe looks vivid and deep on a bright base but lighter and milkier on a full-dull base. Lustre is therefore a TDS parameter that must be fixed before shade approval.
The three lustre classes and typical TiO₂ levels
Industry splits lustre into three representative bands. The TiO₂ weight fractions below are approximate/representative and vary by producer and application; they are not a code standard. Bright (clear & bright) yarn is in practice made with ~0% TiO₂, no delustrant, giving the highest surface shine and the most translucent look. Semi-dull — by far the most common class for apparel knit fabric — typically carries ~0.3–0.5% TiO₂; this is "normal" textile lustre. Full-dull (extra-dull) is loaded with up to ~2% TiO₂ for an almost matte, opaque appearance.
| Lustre class | Typical TiO₂ (representative) | Appearance / opacity | Hand & depth of shade | Typical use |
|---|---|---|---|---|
| Bright | ~0% (no delustrant) | High shine, translucent, low cover | Smooth/cool hand; deepest, most vivid colour yield | Satin lining, glossy sportswear, decorative filament |
| Semi-dull | ~0.3–0.5% | Balanced, natural textile lustre, medium cover | Neutral hand; good depth and repeatability | General apparel knit (single jersey, interlock, rib) |
| Full-dull | up to ~2% | Matte, opaque, high cover, no glare | Softer/fuller hand; colour reads lighter & milkier | Matte activewear, opacity/privacy lining, anti-glare |
Opacity, cover and depth of shade
TiO₂ particles scatter light not only at the surface but throughout the fibre's volume, with two consequences. First, opacity/cover rises: a full-dull fabric transmits less light, so it is favoured for lining and privacy-critical uses (e.g. reducing skin show-through in light-coloured activewear). Second, depth of shade falls: scattered white light mixes with the colour absorbed by the dye, washing out dark tones and making the same disperse recipe read lighter and milkier than on a bright base. In practice the highest colour yield on deep shades — navy, black — is obtained on a bright or semi-dull base; matching that depth on full-dull takes more dye and careful reductive clearing (see the reductive-clearing guide). For colour management and ΔE consistency, lustre class is a variable that must be fixed before lab-dip approval.
Hand and UV behaviour
TiO₂ is also an indirect driver of hand and durability. The delustrant load changes spinning and drawing behaviour and the fibre's surface-optical character; full-dull yarns generally give a softer, less "plastic-shiny" feel. On the UV side, TiO₂ is a known UV scatterer/reflector: delustred (especially full-dull) polyester tends to show somewhat higher inherent UV protection (UPF) than bare bright polyester — but this is a general/representative tendency, not a certified UPF value, and real UPF also depends on construction, GSM, colour and finish. Conversely, TiO₂'s photocatalytic activity can accelerate chain degradation under prolonged UV exposure, so more delustrant does not always mean better outdoor durability; for outdoor uses this trade-off is assessed separately.
Practical takeaway for buyers
- Lustre is a polymer/yarn decision and precedes dyeing — it cannot be changed afterwards, so specify it clearly at sampling and order stage.
- Semi-dull (~0.3–0.5% TiO₂) is the default/safe choice for most apparel knits; choose bright for maximum depth of shade and shine, full-dull for opacity/matte aesthetics.
- The same dye recipe looks different on different lustre bases: bright/semi-dull for deep dark shades, full-dull for a matte & opaque look.
- State the lustre class in the TDS and lab-dip request; ΔE/shade consistency (see the color-management-delta-e guide) is only meaningful on a fixed lustre base.