You aren't incorrect at all Ron. Plastics are used in most all the higher end thermals. Polypropylene to be exact. With the cost of Poly's getting lower, it's starting to be used even in the lower cost long johns although not as high of content nor quality of insulation. While wool is still probably the best as far as insulating factors, your poly cotton blends have what Ron described as "wicking" whereas wool absolutely does not.