Subtractive foam patterning is, needless to say, the opposite of additive foam patterning in that the skin is not added but instead the surface layer or 'skin' is cut away from the positive. Because of its durability, the suggested foam to use to carve the positive is reticulated urethane foam. Reticulated urethane foam is durable and easy to cut. After the positive has been sculpted, the center dividing line and the pattern divisions are drawn, then the top-most layer or skin on the sculpt is cut away to produce the patterns. When learning to pattern foam, the key is to keep designers positive sculpt relatively simple and allow plenty of time for experimentation. Subtractive patterning is a very precise process needing careful and patient cutting skills. The author has used it on several projects and this technique, though painstaking, can produce wonderfully accurate and beautiful pieces.