What a water absorption test shows
Short answer: A water absorption test shows how much water a fabric can take up relative to its own weight. The sample is weighed dry, placed in water, allowed to drip and weighed again. The difference is the number itself.
Why water absorption is measured
How much water a fabric can take in affects how it feels and what it is good for. A towel should absorb, a rain jacket should not. A test puts a number on the property, so fabrics can be compared on a common basis rather than by feel alone.
Weighing before and after
The sample is weighed dry first. Then it is placed in water for a set time and allowed to drip in a consistent way. Finally it is weighed again. The dripping time must be the same every time, or some samples look wetter than others without the fabric being different.
The difference is the whole number
The weight after minus the weight before, divided by the weight before, gives the absorption as a percentage. It is a simple calculation that needs nothing but an accurate scale. A fabric that weighs twice as much afterwards has taken up water equal to its own weight, which gives a hundred percent.
Absorption is not the same as transport
A fabric can take up a lot of water and still be slow to move it on. The two things are measured separately. Absorption is about quantity, while transport is about how fast water spreads or is drawn away. Both are properties, but they do not always behave alike. See Copenhagen Bamboo.
Finishing changes the number
Softening can make a surface less willing to take in water. That is why measurements are made on finished fabric, not on raw yarn or untreated goods. A fabric can behave quite differently after treatment, and the finished fabric is what you actually wear. See Resteröds and Zent.
Time is part of the method
Some fabrics absorb at once, others take minutes. The time is noted in the method so results can be compared. A test that leaves the sample for two minutes does not necessarily give the same number as one that leaves it for an hour. So always look at the number and the conditions it was measured under.
High absorption is not always good
It depends on the use. For a towel, high absorption is good, but for sportswear it is not necessarily an advantage, because a fabric that holds a lot of water can feel heavy and dry slowly. So choose the number to suit the purpose rather than simply going for the highest.
Water absorption and drying time
The number says only something indirect about drying time. A lot of water in the fabric takes longer to evaporate, but drying time also depends on thickness, air and warmth. That is why a separate test is used for drying. Absorption alone does not tell you if clothes dry quickly on the line.
Frequently asked questions
Is high absorption good
It depends on the use. For a towel yes, for sportswear not necessarily. A fabric that takes up a lot of water can also be heavy and slow to dry, so look at the purpose.
How fast does absorption happen
Some fabrics absorb at once, others take minutes. The time is noted in the method so results can be compared. So look at the number together with the conditions it was measured under.
Does the number say anything about drying time
Only indirectly. A lot of water in the fabric takes longer to evaporate, but drying time also depends on thickness, air and warmth. That is why a separate test is used to measure drying.
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