The simulation of glass forming is a complex thermo-mechanical problem. For high temperatures, the mechanical glass behaviour is assumed to be as a viscous incompressible material. Its viscosity is strongly temperature dependent and the process involves large displacements and large strains. Therefore, the finite element modelling of such a process needs to take account of large geometrical transformations. From the numerical point of view, this problem can be studied by means of a solid approach where the degrees of freedom are displacements. This modelling is highly non-linear. Moreover, the numerical convergence can be affected on account of the mechanical contact between the mould and the glass. The aim of this paper is to propose a linear finite element formulation for 3D glass forming where the degrees of freedom are velocity and hydrostatic pressure. The mechanical contact is taken into account by means of an explicit algorithm related to the time integration scheme. The thermal coupling is not considered. The results are discussed and compared to a non-linear formulation where the degrees of freedom are displacements.