How elastic is tested for fatigue
Short answer: Elastic is tested for fatigue by being stretched and released many times in a row. Afterwards you measure how much of it returns. The difference from the original length is the fatigue.
Why elastic gets tired
Elastic in a waistband or cuff is stretched every time you put clothes on, sit down or bend. Over time it loses some of its ability to contract fully again. That is called fatigue, and it is why a waistband can turn slack after many months of use.
The repetition is the test
A single stretch says nothing about durability. It is the many repetitions that show whether the elastic goes slack. That is why the sample is stretched and released a great many times in a machine. It stands in for many days of use in a short time and shows how the elastic will behave later.
Measured after rest
Elastic needs time to contract again. That is why measuring only happens after a set rest period, so you do not misjudge an elastic that is merely a little slow right after the stretch. Otherwise the result would depend on how quickly you measured. See Decoy.
Heat and moisture are included
Some methods test in heat or after washing, because both put strain on the elastic. In real life clothes are washed and dried, and that affects how the elastic copes. A test that takes this into account gives a more honest picture. See Urban Quest and Copenhagen Bamboo.
How much returns
After the test the length is compared with what the sample had before. If it is as short as at the start, the elastic has held up well. If it has grown longer, something has not come back. The difference from the original length is the fatigue, and it can be given as a percentage or a length.
The waistband in daily life
In a waistband the elastic sits snugly all day and is stretched with every movement. That is why the test matters most for underwear and trousers. A waistband that keeps its shape lies flat and does not slip down, while a tired one can feel loose and start to roll.
What wears elastic most
Heat wears it most, both from the tumble dryer and from water that is too hot. Elastic is sensitive to high temperatures, and every time clothes are dried hot, the elastic takes a little damage. Wash at a low temperature and air dry if you want the waistband to keep its shape.
Can a waistband be tightened again
A little, if you wash cold and air dry, but the elastic does not come fully back. Once it has lost some of its power, the damage cannot be undone. Prevention is therefore better than repair. If a waistband is very slack, it can be replaced, or the clothes kept for quieter use.
Frequently asked questions
Why do waistbands go slack
Because the elastic loses some of its ability to contract fully after being stretched many times. Heat from the tumble dryer and water that is too hot speed it up.
Can a waistband be tightened again
A little with a cold wash and air drying, but it does not come fully back. Once elastic has become tired, it is hard to regain full strength, so gentle care is the best approach.
What wears elastic most
Heat, both from the tumble dryer and from water that is too hot. Higher temperatures strain elastic more than low ones, so wash cold or lukewarm and let clothes air dry when you can.
You can find the full range at Bamboo-Clothing.com.
