My first lesson was with wool that was second hand and I was practically a baby. I put the quilt together and later; may have been years; washed the thing only to have a few blocks suddenly half the size. What a puckered mess. If I had known I would have washed all and then know the finished size. Now I felt all the time. Most books recommend Ivory soap and definitely no softener. When you felt a sweater or a crocheted item that you make it can get so strong that no pencil can even puncture it. Works great for the handbags I design and make.