  We introduce a generalization of Mobius energy for knots to an energy
functional for tubular neighbourhoods of closed inextensible curves. We prove
the continuity of the energy and its boundedness for physically admissible
tubes without self-contact and in particular for the torus. The functional
allows to distinguish isotopy classes of the centerline through its physical
inspiration to a self-repulsive electrostatic energy. If the tube has zero
thickness, O'Hara's functional is recovered. Finally, a discussion on the
possible exponents in the functional is carried out.
