Color fastness: the parameters that matter for nylon yarn

A color can be perfect right after dyeing and then disappoint after a few washes or a few weeks of light exposure. Color fastness measures exactly this: how well the color resists the stresses the finished product will be subjected to.

What is measured

Fastness tests are standardized (mainly the ISO 105 series) and rated on a grey scale that generally runs from 1 (poor) to 5 (excellent); the exception is light, rated on a 1–8 scale. The most relevant parameters for nylon yarn:

Light fastness: resistance to fading from light exposure. Critical for items on display.
Wash fastness: resistance to color bleeding and to staining of adjacent fabrics during washing.
Water fastness: resistance to the action of water.
Perspiration fastness: relevant for garments in contact with the skin, assessed in both acid and alkaline conditions.

How we handle fastness at Nyfil

Fastness control is part of our process, not an occasional step:

On standard colors we carry out fastness tests internally on a sample basis on every dye batch.
On special colors — fluorescents, or very deep and bright shades — we always test fastness before sending the batch to coning, because these are the most demanding shades to fix.

The level we aim to achieve is a fastness of 4 / 4.5 on the rating scale. The tests we usually carry out are: acid perspiration, alkaline perspiration, washing, water and light.

For customers who need certified fastness, we rely on external laboratories we work with: this way we can provide a result certified by a third party, in addition to our internal control.

What it depends on

Fastness is not just a matter of "good dye". It depends on:

the choice of dye relative to the material (a dye suited to nylon, well fixed);
correct exhaustion and fixation of the dye bath;
the final washes that remove unfixed dye (essential for wet fastness);
the depth of shade: very deep shades and certain color families are inherently more demanding — which is why we check them systematically.

What matters for each sector

The tests we run cover the real needs of the segments we serve:

Sock and underwear manufacturers: skin contact and frequent washing put perspiration (acid and alkaline) and washing first.
Narrow-fabric (tape) manufacturers: for tapes in contact with the skin, such as those for underwear, perspiration and washing matter most.
Technical and medical: color consistency and reliability are stringent requirements, and this is the segment where external certification most often makes the difference.

In summary

Talking about color without talking about fastness is incomplete. For the buyer of dyed nylon yarn, knowing how fastness is controlled — on a sample basis for standards, systematically for difficult shades, with the option of external certification — means being able to predict how the finished product will behave. It is an element of quality just as much as the shade itself.