A thread is made by spinning together many different fibers. In a finished spun thread, the fiber lies flat. During weaving or knitting, the fiber will be held down by being regularly ironed under the process. In use, the fiber is subjected to friction from other clothing, bags, chair seats or arms and legs that move. This can cause the fiber to loosen from its thread, and the smooth movement rolls the loose fiber together into a small ball or stud.

Some people experience more pilling than others. If you are warm it may cause the fiber to lift a little extra. That's because the wool fiber is programmed to tell if it gets hot to make a ventilating air room. Pilling does not mean that it is poor quality. If the wool fiber is particularly smooth and fine, such as cashmere or angora, it slides more easily out of its thread. The wool, on the other hand, is coarse and curly and in addition hard knitted or woven, it is more necessary for the fiber to loosen and snag. If you are afraid that a garment will start to pill, you need to think about how you use it. Choose a jacket that is smooth and avoid suede bags.

If you use a pilling-knife, the garment will look nice longer. If you iron the wool after washing, the fiber will lay down and it will not pill so fast.