  In Ultra high energy collisions, the concept of a glass law is invoked in the
framework of 'low tension' QCD strings. It is shown that the excitation of QCD
strings at low energy has a negative temperature and at high energy has a
positive temperature always higher than the Hagedorn temperature, T_H. Very
high energy strings T->T_H + 0+ move very slowly as a viscous melted glass with
very high viscosity. However, in a very short collision time, it is difficult
to transfer the initial collision kinetic energy into the internal energy of a
few strings. The low energy strings at high T>>T_H have a low viscosity giving
rise to an almost perfect fluid. The role of strings in a nucleus is closely
analogous to the role of polymer chains in some viscous glass beads.
