Short answer
Polyester is water-repellent and has no charged sites, so it is dyed with disperse dyes — small, barely soluble molecules that dissolve into the fibre at high temperature — or coloured by pigment added to the molten polymer before spinning. Nylon takes acid dyes and acrylic basic dyes. Because these dyes have different absorption spectra from the reactive dyes on cotton, a polyester and a cotton matched under one light often mismatch under another. Lustre, delustrant and fibre shape also change how the colour looks.
Relative to other materials in this section, not a measurement of a particular product.
| Process | What you see | Driven by | Slowing it |
|---|---|---|---|
| Dye migration and sublimation | Colour transferring to adjacent fabric or prints | Heat mobilising disperse dye | Heat-set properly; avoid over-hot ironing and drying |
| Pilling and surface abrasion | Fuzzy, lighter-looking surface | Fibre ends working out and scattering light | Filament yarns or anti-pill finishes |
Polyester's tightly packed, hydrophobic chains leave no room for water-soluble dyes. Disperse dyes, developed in the 1920s for cellulose acetate, are non-ionic molecules with very low water solubility, used as a fine dispersion. Heated — typically above the boil in pressurised machines — the fibre structure opens, the dye dissolves into the polymer and is held by van der Waals and dipole forces as the fibre cools. Most are azo or anthraquinone types. Because the dye is dissolved in the fibre rather than bonded to it, heat can make it move again: over-hot ironing, heat-setting or tumble drying can sublime dye onto neighbouring fabric or printed transfers, and dark polyester sportswear can migrate dye into white prints on it.
An alternative to dyeing is to colour the polymer itself: pigment or masterbatch is added to the melt before extrusion, so every fibre is coloured throughout — solution-dyed or dope-dyed fibre. It is very fast to light and washing, uses no dyebath, and is common in outdoor fabrics, carpets and car interiors, but colours must be made in large lots and cannot be changed later. At the other extreme, sublimation printing exploits disperse dyes' mobility: images printed on paper with disperse inks are transferred into polyester by heat, giving photographic prints for sportswear and banners. Such prints only work well on white or pale polyester, since the dye adds to the fabric's colour.
Melt-spun polyester and nylon filaments are smooth, transparent rods, so untreated they are glossy and slightly translucent. Titanium dioxide is added as a delustrant to scatter light inside the fibre, giving 'bright', 'semi-dull' and 'full-dull' grades that differ in lustre and in how deep the same dye looks. Cross-section shapes — trilobal, hollow, microfibre — change sparkle and scattering: trilobal fibres glint like silk, microfibres have many surfaces and look softer and paler for the same dye content, needing more dye for depth. Brushing and pilling raise fibre ends that scatter white light, so worn polyester fleece looks lighter and duller than new.
A polyester–cotton blend needs two dye classes, one for each fibre, and the two must be balanced to look like one colour; under another light, the different dye spectra can separate them into a two-tone effect. Separate polyester and cotton garments matched to the same standard frequently show illuminant metamerism: fine in the showroom, not in daylight. Nylon and wool share acid dyes but take them at different rates. Acrylic, dyed with basic dyes, can give very bright colours that other fibres cannot reach. For product ranges with mixed fibres, colour approval under at least two light sources, and against a physical standard rather than a screen or a number alone, is the practical safeguard.
Why: Disperse dye migrating into the print under heat.
Fix: Use low-migration dyes and blocker inks; avoid hot tumble drying.
Why: Metamerism between disperse and reactive dyes.
Fix: Approve against a standard under daylight and a warm lamp.
Why: More fibre surface scatters more white light.
Fix: Use a deeper recipe for fine-denier fibres.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactModerate evidence
Disperse dyes are non-ionic, sparingly water-soluble synthetic dyes for polyester and related hydrophobic fibres, held in the polymer by van der Waals and dipole forces; they were introduced in the 1920s and diffuse better at and above the boil.
Source: Disperse dye
FactModerate evidence
Polyester is dyed with disperse dyes, nylon with acid dyes and acrylic with basic dyes.
Source: Dyeing
Colourwise interpretationModerate evidence
Different dye classes on different fibres commonly produce illuminant metamerism, so fabrics matched under one light can mismatch under another.
Based on: Follows from the different absorption spectra of disperse, reactive and acid dyes; see the lighting-science pages on metamerism.
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.