This paper presents a physically based method to deal with haptic feedback of manipulated deformable virtual objects in contact with rigid or deformable environment. The haptic rendering algorithm is based on the Signorini's formulation of the contact as proposed in theoretical mechanics. Since haptic interaction requires high refresh rates, a multi-threaded methodology, sharing con.guration values of the contact, ensures good stability and transparency performances. Thus, the interactive simulation gathers three synchronized process: the visualization process, the deformation/contact computation process, and the haptic rendering process.