Luster
Also searched as: lustre, sheen, gloss, shine, delustered
The sheen of a fiber, yarn or fabric, produced when smooth surfaces reflect light in a concentrated, mirror-like direction instead of scattering it diffusely, which would give a matte look.
In detail
Luster depends on how light meets the fiber surface and interior. Smooth, regular surfaces send more light in one concentrated direction, producing highlights, while rough surfaces and internal interfaces scatter light in many directions and look flatter. In wool, the size and profile of cuticle scales affect surface reflection. Internal air spaces also matter: heavily medullated fibers scatter so much light that they look chalky white. Yarn twist, fabric construction and finishing then modify how the fiber's luster reads in a garment, so the same fiber can look bright in one cloth and subdued in another.
The science and numbers
Surface reflection follows the Fresnel relations: at a smooth interface between air and a polymer with a refractive index near 1.5, only about 4% of light reflects specularly at normal incidence, with the fraction rising toward grazing angles, and the rest enters the fiber. Inside, interfaces such as air-filled medulla cells or pigment particles scatter light diffusely. Luster therefore increases when surfaces are smooth and flat compared with the wavelength of light and decreases when roughness or internal scatterers are present. In wool, heavy medullation raises light reflection and produces a white, chalky appearance, and studies quantify cuticle scale morphology as a surface parameter. Instrumental luster is commonly assessed by goniophotometry, which compares specular with diffuse reflectance over a range of angles.
A practical example
A class drapes two fabrics made from the same fiber under a single lamp: a satin weave with long floats and a plain weave. As each is tilted, the satin shows bright, moving highlights, while the plain weave looks flatter. Students conclude that luster is partly a property of construction, because long, parallel floats present a more continuous reflecting surface than short, frequently interlaced yarns.
What to distinguish
Luster describes appearance, not quality, softness, cleanliness or fiber content. Luster also differs from color and whiteness: a white fabric can be matte and a dark one glossy. Shine that develops on worn dark garments at elbows or seats comes from surfaces flattened by abrasion or pressing, an unwanted luster caused by use rather than a property of the original fiber.
Origins and history
The English word, spelled lustre in British usage, shares its root with the French lustre and the Italian lustro and ultimately with Latin words for light and brightness. Textile trades have long used it for the sheen of silk and of smooth, long wools. With manufactured fibers, luster became a design variable, because producers could make filaments brighter or duller through their choice of cross-section and additives.
Related terms
Sources & further reading
- SGS Wool Testing Services: Info bulletin 5.4B, medullation
- Scientific Reports: Novel parameters for characterising scale morphology of wool fibre and correlation with dye diffusion coefficient of acid dye
- Woolwise: Structure of the fibre (course notes)
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.