Felting is a method of creating strong and stable fabric out of knitted fabric, which is generally very stretchy.
How to Felt Knitted Fabric:
Put felt project into a zippered pillowcase or other closed bag. Using hot water, set the washing machine for a heavy cycle, with the water level set for a small load. Add felt project, soap and an old pair of jeans or athletic shoes. Fill machine and begin agitating. It takes about 10 minutes for anything to happen and the felting process may require resetting to beg of cycle. Once felting begins, check and measure frequently to achieve the finished size. Finish rinse and spin cycles then take the piece out, pinch it into the proper shape and let it dry.
Note: Felting is inexact at best. Variations in final results may occur based on gauge, yarn color, water temperature, washer agitation, and softness or hardness of water; all measurements given are only approximations. The best control is to check felting progress often after the first 5-7 minutes of felting. If it appears more agitation is needed, reset the cycle to the beginning and continue to monitor.