  Many minimal models of dark matter (DM) or canonical solutions to the
hierarchy problem are either excluded or severely constrained by LHC and direct
detection null results. In particular, Higgs Portal Dark Matter (HPDM) features
a scalar coupling to the Higgs via a quartic interaction, and obtaining the
measured relic density via thermal freeze-out gives definite direct detection
predictions which are now almost entirely excluded. The Twin Higgs solves the
little hierarchy problem without coloured top partners by introducing a twin
sector related to the Standard Model (SM) by a discrete symmetry. We generalize
HPDM to arbitrary Twin Higgs models and introduce Twin Higgs Portal Dark Matter
(THPDM), which features a DM candidate with an $SU(4)$-invariant quartic
coupling to the Twin Higgs scalar sector. Given the size of quadratic
corrections to the DM mass, its most motivated scale is near the mass of the
radial mode. In that case, DM annihilation proceeds with the full Twin Higgs
portal coupling, while direct detection is suppressed by the pNGB nature of the
125 GeV Higgs. For a standard cosmological history, this results in a predicted
direct detection signal for THPDM that is orders of magnitude below that of
HPDM with very little dependence on the precise details of the twin sector,
evading current bounds but predicting possible signals at next generation
experiments. In many Twin Higgs models, twin radiation contributions to $\Delta
N_\mathrm{eff}$ are suppressed by an asymmetric reheating mechanism. We study
this by extending the $\nu$MTH and $X$MTH models to include THPDM and compute
the viable parameter space according to the latest CMB bounds. The injected
entropy dilutes the DM abundance as well, resulting in additional suppression
of direct detection below the neutrino floor.
