I have been making mittens. Lots and lots of mittens. There isn’t a thrift store in my area that still has any pretty wool sweaters because I have bought all of them! All of the wool is washed in hot water and dried on the highest heat my drier can manage. This produces felted wool which doesn’t fray when cut and is very water resistant which is perfect for mittens. I use polar fleece for the linings so these mittens keep your hands warm and toasty.
Want to felt some wool? Try using this tutorial.