Integral field spectroscopy of the GQ lup companion Only few ultra low mass substellar objects are currently observed in their earliest stages of formation. Their exact formation process is only poorly understood and a matter of debate. Evolutionary models oversimplify the initial conditions and are highly speculative for objects up to a few Myr of age. The spectral properties of such objects are hard to model. At extremely low temperatures and low surface gravities complex molecular chemistry and dust formation challenges theoreticians to compute synthetic spectra of high reliability. The extreme scarcity of anchor points objects whose mass and radius can be measured directly enhances the difficulties in properly describing and classifying such objects.