Moment equations offer an attractive framework for modeling non-equilibrium processes in moderately rarefied gases. We present a new hyperbolic closure for the 5-moment system in the one-dimensional setting that couples the conservation laws of mass, momentum and energy to two evolution equations of higher, non-equilibrium moments. The new closure, given in closed-form, depends on a regularization parameter β that is related to the non-linearity around the equilibrium state, so as to mitigate the appearing sub-shock in the continuous shock-structure problem.We consider the one-particle phase space f :where c denotes the microscopic velocity, such that n(x, t) = f := R f (x, t, c) dc is the particle density. Moments of the distribution function f over velocity space yield macroscopic quantities such as the mass density ρ = m f , macroscopic velocity v = m cf /ρ or temperature θ = m C 2 f /ρ in energy units, where C = c − v denotes the random velocity and m is the particle mass. We use the simplified BGK operator [1] to model the effect of particle collisions. The evolution of f is then described by the Boltzmann BGK equation(1) denotes the local Maxwell-Boltzmann equilibrium distribution function and τ is the relaxation time. We further define the higher non-convective moments Q = m C 3 f , R = m C 4 f , S = m C 5 f , such that q = Q/2 is the physical heat flux. For any fixed time t and position x, the distribution function, f , can be normalized by the mapping f (c) = (n/θ, such that the normalized momentsû = ξ if with i = 0, . . . , 4 are given byû = (1, 0, 1,Q,R) T , whereQ = Q/(ρθ 3/2 ),R = R/(ρθ 2 ). Let u = (ρ, v, θ,Q,R) T denote the vector of field variables, then we can express the convective moments as E i (u) = c i f for i = 0, . . . , 4. The projection of equation (1) on these convective moments yields the 5-moment system in balance law formIn order to close the 5-moment system a constitutive relation between the non-convective momentŜ = S/(ρθ 5/2 ) and the field variables u is required. Such relations can be found by the postulation of a model distribution function,f (Model) , parameterized so that the moment constraints ξ if (Model) =û i for i = 0, . . . , 4 uniquely determinef (Model) and thus alsô S = ξ 5f (Model) . The now classical closure proposed by Grad in [2] is based on a Hermite expansion of the distribution function in velocity space, which yields the simple closureŜ (Grad) = 10Q for the 5-moment system. Unfortunately, the resulting system is only hyperbolic for small deviations from the local equilibrium distribution, greatly limiting the range of processes that can be modeled with Grad's closure.Closures based on the maximization of the physical entropy have been proposed [5,8]. While these closures yield globally hyperbolic systems, the evaluation of the closing fluxes requires the use of computationally expensive optimization methods if the equations include terms higher than the second moment [4][5][6].Recently, a closed-form closure for the 5-moment equations, featuring some character...