Felting wool can happen accidentally, for example by washing too hot.
Felting wool is sometimes also called fulling (with woven fiber). Earlier this happened in fulling mills. For felt wool of inferior quality can be used. After carding the wool is deposited crosswise into two (or more) layers on each other. Then the wool is rubbed with warm water and soap. Wool can absorb a lot of water and is thus elastic and stretches. If you then rapidly cool the wool and move it, the scales remain stabbing at the fiber surface together. If some spots are weaker you have to put the right supplement for uniform thickness.
By kneading constantly the barbs of the wool fibers grasp together and the water is squeezed from the wool whereby felt is created. Press and knead on two sides. The felt has to be finally pressed flat and in model. Anticipate to a shrinkage of 30 to 50%.

You can also use plant soap. Ivy also contains saponin. Of these, the leaves are collected and boiled for about 10 minutes in a little water. Warning: saponins are poisonous so be cautious!

You can also use hare en fur for felt.