A new process combining incremental sheet forming and the use of an active medium to produce concave-convex geometrical parts is introduced. Both, experiments and finite element modeling, pursue the objective of explaining the basic forming mechanism and of discussing the influence of the active medium pressure on the overall process feasibility. Results show that the active medium, in this case gas, acts as an active supplementary tool under controlled pressure, thus enabling the manufacture of concave–convex parts which could not be easily produced by conventional incremental sheet forming.