I have to agree with crashnquilt. Thread is no different than any other product that we use. When Poly first came out, it was a different "animal". Just like our fabric has evolved, so has our thread, cutting methods, machines, etc. Would you use Poly thread from the 70's? Probably not any more than you would use cotton thread from the 70's. Everything evolves. Remember that cotton thread has evolved too. Use what you are comfortable with. If you're not sure, make 2 doll quilts, one using cotton, one using Poly. Wash them each several times together, and see which result is better. If there isn't any difference, you have your answer. If there is a difference, you have your answer.