  We present evidence, from Lattice Monte Carlo simulations of the phase
diagram of graphene as a function of the Coulomb coupling between
quasiparticles, that graphene in vacuum is likely to be an insulator. We find a
semimetal-insulator transition at $\alpha_g^\text{crit} = 1.11 \pm 0.06$, where
$\alpha_g^{} \simeq 2.16$ in vacuum, and $\alpha_g^{} \simeq 0.79$ on a
SiO$_2^{}$ substrate. Our analysis uses the logarithmic derivative of the order
parameter, supplemented by an equation of state. The insulating phase
disappears above a critical number of four-component fermion flavors $4 <
N_f^{\text{crit}} < 6$. Our data are consistent with a second-order transition.
