Colour fastness numbers and how to read them
Short answer: Colour fastness is also given as a number from one to five. It tells you how well the colour holds up to washing, sweat, rubbing and light, and there is a number for each. Here is how to read the numbers and what they mean for your clothes.
One number per exposure
A fabric may have four for washing, three for rubbing and five for sweat. The numbers are not linked, and a low number in one place says nothing about the others. Look at all the numbers, not just one, to see how the colour behaves in daily life. It is like several grades rather than one overall mark.
Light fastness uses another scale
Light is measured from one to eight instead of one to five. Eight means the colour hardly changes, even after a long time in the sun. The scale is longer because light acts slowly and in many steps. See our bamboo polos for men, where you see the colour every day.
The four exposures
Wash fastness shows whether the colour stays in the fabric in water. Sweat fastness shows whether it holds against sweat and skin. Rub fastness shows whether it transfers when the fabric rubs against something else, dry or wet. Light fastness shows whether it fades in the sun. Each answers one practical question.
What the numbers mean for you
Low rub fastness means the colour can transfer onto light furniture. Low wash fastness means the garment should be washed on its own. The numbers can therefore make care easier if you read them well. See also home and homewear in bamboo and Nordic Weaving.
Why dark colours are often lower
Dark colours carry more dye in the fabric, and loose dye can transfer. That does not make dark clothing poor, only more likely to need separate washing at first. Over time and after a few washes the transfer often eases, and the colour becomes more stable.
What counts as a good number
Four or above counts as good for wash fastness in ordinary clothing. The same rule of thumb applies to rubbing and sweat, but the requirement may be higher for light textiles or anything rubbed a lot. There is no single right answer, so read the number in light of how the garment is used.
Where the numbers come from
The numbers come from standardised tests. The sample is washed, rubbed, exposed to sweat or lit by a fixed method, and the colour is then compared with a scale. That lets numbers from different fabrics be compared. Customers rarely see them, but they are typically used in the factory quality control.
How to slow colour loss
You cannot improve colour fastness itself, but you can slow the loss. Wash cool, use a mild detergent, turn the garment inside out and avoid long spells in direct sun. Wash new dark pieces on their own the first few times. The colour then stays nicer for longer, and other items stay clear of stains.
How to use the numbers
Use the numbers as an aid in choosing and caring for clothes. If rub fastness is low, keep the garment away from light furniture. If wash fastness is low, wash it on its own. If light fastness is low, do not leave it in the sun. Simple habits often give the best results over time.
Frequently asked questions
What is a good number for wash fastness
Four or above counts as good in ordinary clothing. It is a rule of thumb, and the requirement may be higher for light colours or textiles that are washed often.
Why are dark colours often lower
Because there is more dye in the fabric and the loose dye can transfer. It is wise to wash new dark pieces on their own the first few times.
Can I improve colour fastness
Not in itself, but you can wash cool and avoid sun to slow the loss. That keeps the colour looking good for longer.
You can find the full range at Bamboo-Clothing.com.
