On this page
Short answer
Light-fastness is how well a fabric's colour resists fading in light. It is usually tested by exposing a sample to artificial daylight beside eight blue wool references, and rated from 1 (fades very quickly) to 8 (outstanding), with each step taking roughly twice the exposure of the one before. For curtains, look for 5 or higher, and 6 or more on sunny windows; outdoor fabrics need 7 or more. Linings, sheers and mid-tone colours slow fading further.
What light-fastness measures
Sunlight, and to a lesser extent indoor light, slowly breaks down the dyes in a fabric. Light-fastness is the fabric's resistance to that colour change. It is one of several colour-fastness properties, and the one that matters most for curtains and for sofas near a window.
Light also slowly weakens fibres, which is a separate effect: a fabric can keep its colour and still become brittle after years of strong sun, especially natural fibres. Lining protects against both.
How the test works
In the common international method (ISO 105-B02), a fabric sample is exposed to a xenon arc lamp, which imitates daylight through window glass, alongside a set of eight standard blue wool cloths. Part of the sample is covered so the faded and unfaded areas can be compared.
Each blue wool reference fades at a known rate, and each takes about twice as much light to fade as the one before. The fabric's rating is the number of the blue wool reference that faded by the same amount. So a fabric rated 6 holds its colour about twice as long as one rated 5.
Good to know
Some specifications, especially from the US, quote light-fastness as hours of exposure under a different method rather than a Blue Wool number. Compare ratings from the same test.
The Blue Wool scale, 1 to 8
| Rating | Light-fastness | Typically suits |
|---|---|---|
| 1 to 2 | Very low to low | Not suitable for windows |
| 3 | Moderate | Cushions and trims away from the sun |
| 4 | Fairly good | Upholstery and curtains in rooms with little direct sun |
| 5 | Good | Most curtains and upholstery in homes |
| 6 | Very good | Sunny and west-facing windows, hotels and offices |
| 7 to 8 | Excellent to outstanding | Outdoor fabrics, awnings and sunshades |
These are general guides. A project specification, or a supplier's own recommendation, takes priority.
Light-fastness and the other colour-fastness tests
| Test | What it checks | Scale | Matters most for |
|---|---|---|---|
| Light | Fading in daylight | Blue Wool, 1 to 8 | Curtains, sofas near windows, outdoor |
| Rubbing (crocking) | Colour rubbing off onto other surfaces, dry and wet | Grey scale, 1 to 5 | Upholstery, especially dark colours |
| Washing | Colour loss and staining in the wash | Grey scale, 1 to 5 | Curtains and covers that are washed |
| Water | Colour bleeding when wet | Grey scale, 1 to 5 | Kitchens, bathrooms, outdoor |
On the grey scales, 5 is best. Rub fastness also explains why new dark jeans can mark a pale sofa: the dye rubs off the denim, not the sofa. See Martindale Rub Test for abrasion resistance, which is a different property again.
Why fabrics fade faster in Malaysia
- Strong sun all year. Close to the equator, the sun is intense in every month, so a curtain gets a year's heavy exposure every year.
- Window direction. West-facing windows get the hot afternoon sun and fade fastest; east-facing ones get the morning sun.
- Exposed folds. The edges and folds left in the sun when the curtain is open fade first, which is why the leading edge often fades before the rest.
- Fibre and dye. Solution-dyed fibres, coloured before they are spun, fade least. Dyed polyester generally holds its colour better than cotton, linen or silk.
- Colour. Very bright and very dark shades show fading soonest; mid-tones and greys hide it best.
See Outdoor Fabric: Solution-Dyed Acrylic for why solution-dyed fibres resist the sun.
How to slow fading
- Line the curtain. A lining takes the sun instead of the face fabric. See Curtain Lining.
- Add a sheer. A sheer on a double track filters the sun during the day. See Sheer Curtains.
- Close the curtains in peak sun, on west-facing windows in the afternoon.
- Use window film or UV-filtering glass for rooms with valuable fabrics.
- Rotate and swap sofa cushions so they fade evenly.
Tip
Ask for the light-fastness of the exact colourway you are buying. Ratings are measured per colour, and two colours of the same collection can rate differently because they use different dyes.
Solution-dyed outdoor fabrics
The JOTEX OUTDOOR collections made from solution-dyed acrylic, the most fade-resistant construction, for terraces, balconies and poolside use. Updated from the catalogue.
Browse outdoor fabric →
Frequently asked questions
What is a good light-fastness rating for curtains?
5 or higher on the Blue Wool scale for most curtains, and 6 or more for sunny or west-facing windows. Outdoor fabrics need 7 or more.
What does Blue Wool 5 mean?
The fabric faded as much as blue wool reference 5 under the same light. That is rated good, and holds colour about twice as long as a fabric rated 4.
Do polyester curtains fade?
Every dyed fabric fades eventually in strong sun, but polyester generally holds its colour better than cotton, linen or silk. A lining and a sheer slow fading further.
Does a lining stop curtains fading?
It greatly slows it, because the lining takes the direct sun instead of the face fabric. The exposed edges and folds can still fade over time.
What is the difference between light-fastness and colour-fastness?
Colour-fastness is the family of tests; light-fastness is one of them. Others cover rubbing, washing and water. Light-fastness uses the Blue Wool scale from 1 to 8, the others a grey scale from 1 to 5.
Why did only part of my curtain fade?
The parts left in the sun fade first: the leading edges and the folds that face the window when the curtain is open. A lining, and closing the curtains in the hottest sun, slow it down.
Curtain maker, upholsterer or designer?
Specifications are public on every collection page. JOTEX dealers can log in for live stock and pricing, and our team can send samples or open a dealer account.