I agree with Silver. Use any aran or worsted weight wool you want. Some wools are labeled 'superwash' and can be washed in the machine, but must be laid flat to dry. Acrylics can be washed and dried. There are blends that are usually 75% acrylic and 25% acrylic that are machine washable and dryable.
Patterns will often list a yarn to use because either that is what they used for the sample in the picture, or the pattern is put out by a certain yarn company and they, of course, want you to use their product.