Sun bleaching on merino wool: how to spot it and prevent it

Why does clothing bleach in the sun?

Wool fibres and textile dyes break down when they sit in direct sunlight for longer periods. Dark and saturated colours show it most clearly. Sun bleaching is not a fault in the fabric or the dye. It is the chemistry of light, and it affects all dyed textiles, wool as well as cotton.

How to recognise sun bleaching

The fading follows the light, not the wash. If the garment hung folded over a clothesline, you will see a clear edge where the fold was, with one half lighter than the other. The side that faced the sun is the most faded, while the side facing away often keeps close to its original colour. You may also see irregular, lighter streaks where the fabric was damp with sweat or water while it hung in the sun.

The colour is gone from the fibres themselves. There is no residue or stain to feel. This makes it easy to tell apart from detergent spots, which are small and concentrated, and from ordinary wear, which fades the fabric evenly without sharp edges.

Faded merino T-shirt with a sharp colour boundary and irregular pinkish areas
Sunlight: The sharp boundary shows where one area of fabric has been more exposed to light than the other. Sweat and moisture: The irregular pinkish areas are consistent with moisture intensifying the fading.

Why the fading is worst where you sweat

Sweat is mildly acidic and leaves salts in the fabric. If a t-shirt is hung to dry with sweat still in it, those areas bleach faster and more unevenly than the rest. That is why the fading often shows exactly where you sweat the most, typically on the chest and back.

Merino T-shirt with a dark protected inside and a sun-faded purple outside
Sunlight: The dark, protected inside contrasts with the faded outside. Sweat: During active use, moisture and salt can make fading develop faster and less evenly.

Can it be removed?

Unfortunately, no. The colour has been broken down by light, it is not dirt sitting on top of the fabric. No wash, rinse or treatment can bring it back. The damage is purely cosmetic, though. Breathability, function and strength are unaffected, and the garment works just as well as before.

How to prevent it

Rinse sweat out before you hang the garment to dry. A quick rinse in lukewarm water is enough after a sweaty day. Dry in the shade or indoors, merino dries fast and does not need direct sun. Hang the garment on a hanger or dry it flat instead of folding it over a line, so you avoid hard bleach edges if it does catch some sun. If it has to hang outdoors, turn it inside out and let the inside take the light.

Is it covered by warranty?

Sun bleaching is caused by wearing in the sun, sweat and drying in direct sunlight and is not a product defect. Like all dyed textiles, merino cannot withstand hours of direct sun. If you are unsure what has happened to your garment, write to us with a few photos and we will take a look together.