http://www.schwalbetires.com/new_high_end.html
"The flexible carcass reduces rolling resistance by approximately ten per cent"
This is pretty much what I keep on reading about. Those tests in german magazines like tour for example also
tend to have higher TPI tires come out with lower rolling resistance.
Obviously the design of the tire as whole matters the most, but the flexibilty of the tire carcass is one factor that plays into the whole picture.
Here is an answer form Leonard Zinn (scroll down)
http://www.velonews.com/tech/report/...es/7508.0.html