Numerical simulation of the airbag can be used as a powerful tool in the development of a SIR (Supplemental Inflatable Restraint) system leading to an optimized design and to reduce the development time. However, modeling flattened or folded airbags from the 3D CAD geometry and simulating exact airbag shapes during the deployment is a very complex problem. Especially for the passenger side airbags, generating a flattened and folded mesh from the CAD geometry of the airbag is a very difficult task as these airbags are made of non-developable surface and can not be flattened easily without introducing secondary folds, wrinkling or distortions of mesh. A novel approach called as Initial Metric methodology effectively addresses these problems. The initial metric method uses two types of meshes, A CAD reference mesh and a mapped or a scaled (compressed) mesh constructed from a CAD mesh of the airbag. In the simulation, mapped or scaled (compressed) mesh is used for airbag inflation. An initial metric algorithm calculates internal forces based on geometric differences between the reference mesh and mapped mesh and applies them to the mapped airbag to produce a geometrically correct airbag. The inflation of this geometrically correct airbag is more accurate. Initial metric method can also result in significant (approximately 70-80%) amount of saving in time as mapped meshes are easier to create. Also, the same mapped mesh can be used repeatedly for different simulations with minor changes to CAD or to a reference airbag mesh.