How dye binds to a fibre

Short answer: Dye either bonds chemically to the molecules of the fibre or lodges physically in the pores of the fibre. The chemical bond lasts longest, and it decides whether a colour stays clear after many washes or slowly turns dull.

What happens in the dye bath

When fabric is dyed, it sits in a bath of dye dissolved in water. The fibres absorb the water and swell slightly, letting dye molecules move in. What happens next depends on the fibre and the dye. Some molecules attach with a real bond, while others simply stay in the gaps and pores of the fibre.

A chemical bond is strongest

Reactive dyes form a true chemical bond with the fibre and do not wash out. The dye molecule effectively becomes part of the fibre. This is the type used for viscose in bamboo t-shirts for women. Viscose is made from cellulose just like cotton, so the same reactive dyes suit both fibres.

A physical bond lets go more easily

Some dyes only hold on mechanically and rinse out gradually in the wash. They stay in the fibre because they are trapped, not because they are bonded. Each time the fabric is wet and moved, a little more escapes. You see it as fading, for example on bamboo joggers for women.

What breaks the bond

Heat, chlorine and strong alkali attack the bond and loosen the colour. Heat opens the fibres, chlorine destroys the dye molecule itself, and strong alkali can break the link between dye and fibre. That is why cold washing keeps colour longest, including on bamboo panties that are washed often.

Why dark colours need more

A black or navy fabric needs far more dye in the same amount of fibre than a light one. The more that has to go in, the harder it is to bond all of it. So dark shades often fade a little more visibly. That is not necessarily poor quality, just a result of the amount of colour.

Protecting colour in the wash

Wash at thirty degrees, use a liquid detergent for colours and avoid products with bleach. Turn clothes inside out so the surface does not rub against the drum. Do not fill the machine completely, and choose a gentle programme with a lower spin. That spares both the fibre and the bond between dye and fibre.

Drying and storage

Colour is affected after washing too. Dry clothes in the shade or indoors, since sunlight can break down dye molecules. Do not leave wet laundry in a pile, as loose dye can move from one item to another. Store clothes in a wardrobe or drawer away from direct light.

Frequently asked questions

Can you tell which type of dyeing was used

Not directly, but an item that fades a lot in the first washes is often physically dyed. A chemically dyed item usually loses only a little surplus dye at first and then stays stable.

How many washes does good dyeing last

More than fifty at thirty degrees without bleach. How long it lasts in practice also depends on drying, sunlight and how the garment is otherwise treated.

Are dark colours harder to bond

Yes, because far more dye has to go into the same amount of fibre. That makes washing dark clothes cold and inside out especially important.