  We show that thin rectangular ribbons, defined as energy-minimising
configurations of the Sadowsky functional for narrow developable elastic
strips, have a propensity to form spherical shapes in the sense that forceless
solutions lie on a sphere. This has implications for ribbonlike objects in
(bio)polymer physics and nanoscience that cannot be described by the classical
wormlike chain model. A wider class of functionals with this property is
identified.
