We report experimental and theoretical studies of double droplets produced in PDMS microfluidic systems. The long term observed morphologies (complete engulfing, partial engulfing and non-engulfing) are solely controlled by fluid interfacial energies and therefore can be predicted independently of the geometry and the surface properties of the microsystem. Non equilibrium long live double droplets, impossible to produce with standard techniques, are also produced under excellent control. A theoretical model estimates the lifetime of these structures. The excellent control offered by microfluidic technology opens the way to finely structuring colloidal materials.