  We investigate two classes of inflationary models, which lead to a stiff
period after inflation that boosts the signal of primordial gravitational waves
(GWs). In both families of models studied, we consider an oscillating scalar
condensate, which when far away from the minimum it is overdamped by a warped
kinetic term, a la $\alpha$-attractors. This leads to successful inflation. The
oscillating condensate is in danger of becoming fragmented by resonant effects
when non-linearities take over. Consequently, the stiff phase cannot be
prolonged enough to enhance primordial GWs at frequencies observable in the
near future for low orders of the envisaged scalar potential. However, this is
not the case for a higher-order scalar potential. Indeed, we show that this
case results in a boosted GW spectrum that overlaps with future observations
without generating too much GW radiation to de-stabilise Big Bang
Nucleosynthesis. For example, taking $\alpha={\cal O}(1)$, we find that the GW
signal can be safely enhanced up to $\Omega_{\rm GW}(f)\sim 10^{-11}$ at
frequency $f\sim 10^2\,$Hz, which will be observable by the Einstein Telescope
(ET). Our mechanism ends up with a characteristic GW spectrum, which if
observed, can lead to the determination of the inflation energy scale, the
reheating temperature and the shape (steepness) of the scalar potential around
the minimum.
