The Physics of Felting:
What Makes It Happen
Successful felting depends on three conditions:
When wool fibers get moist, their core begins to swell. This causes the fine layer of scales along the fiber surface to open.
The scales open more fully at a higher temperature.
As with a pile of coat hangers, these open scales readily catch onto one another. The more you agitate the materials, the more enmeshed the scales become. The fiber becomes matted and dense, reducing the overall size of the fabric being washed.
Studies have proven that the felting process occurs more readily when the pH level of the water is higher. Adding a small amount of soap to your felting water will help, because it naturally raises the pH level.
Likewise, you can stop the felting process and close the fiber scales by adding a moderate amount of vinegar to your cold-water rinse. This lowers the pH level.
More About Felting