  We discuss a new mechanism to enhance the spectrum of primordial tensor
fluctuations in single field inflationary scenarios. The enhancement relies on
a transitory non-attractor inflationary phase, which amplifies the would-be
decaying tensor mode, and gives rise to a growth of tensor fluctuations at
superhorizon scales. We show that the enhancement produced during this phase
can be neatly treated via a tensor duality between an attractor and
non-attractor phase, which we introduce. We illustrate the mechanism and
duality in a kinetically driven scenario of inflation, with non-minimal
couplings between the scalar and the metric.
