We investigate the statistical mechanics of long developable ribbons of finite width and very small
thickness. The constraint of isometric deformations in these ribbonlike structures that follows from the
geometric separation of scales introduces a coupling between bending and torsional degrees of freedom.
Using analytical techniques and Monte Carlo simulations, we find that the tangent-tangent correlation
functions always exhibit an oscillatory decay at any finite temperature implying the existence of an
underlying helical structure even in the absence of a preferential zero-temperature twist. In addition, the
persistence length is found to be over 3 times larger than that of a wormlike chain having the same
bending rigidity. Our results are applicable to many ribbonlike objects in polymer physics and nanoscience that cannot be described by the classical wormlike chain model.