  QCD strings are color-electric flux tubes between quarks with a finite
thickness and thus a finite curvature stiffness. Contrary to an earlier
rigid-string by Polyakov and Kleinert, and motivated by the properties of a
magnetic flux tubes in type-II superconductors we put forward the hypothesis
that QCD strings have a {\em negative\/ stiffness. We set up a new string model
with this property and show that it is free of the three principal problems of
rigid-strings --- particle states with negative norm, nonexistence of a
lowest-energy state, and wrong high-temperature behavior of string tension ---
thus making it a better candidate for a string description of quark forces than
previous models.
