Okay so I know that they aren't but this thing i am reading makes it appear that they are fixed. QUOTE from the text: "The values of nb(for the statistical segment) chosen in this work are 18 bonds for polyethylene and 24 bonds (a hexamer) for poly(cisisoprene). One reason for these choices of nb involves the concept of the Kuhn statistical length, which, for polyethylene is ,12A°and ,9 A° for poly(cis-isoprene)". So is he trying to say that Kuhn lenghts are fixed? I dont understand. because kuhn lenghts follow this formula: ,h=nL and <h^2>=nL^2 ...which means it depends on the number of bonds 'n' that we chose to work with in the first place.