The fleece pouches are generally designed for cooler climates or for winter - so yes, they are warmer than a cotton pouch. Depending on how far south you are, you may find it good for winter; it would probably be like the difference you'd feel from wearing a light polar fleece jacket to a light to mid-weight cotton jacket. You will probably find it too hot for summer, particularly with a newborn. I don't know that I'd use the analogy that fleece is used in nappies (sorry Mel!) - because the nappy only covers a small amount of the baby's body, whereas a carrier, especially a pouch if the newborn is in a cradle carry, covers the whole body. So it's going to be warmer by comparison just by coverage alone.