From respirator lung to ventilator induced lung injury, we have travelled a long distance from the concept of barotrauma-volutrauma to stress-strain. Stress is defined as equal and opposite force developed in a material, when exposed to external force, while strain is change in the area or volume from baseline, brought about in this process. Stress-strain relationship is a function of material property, solid, viscous or viscoelastic. Current strategy of mechanical ventilation as endorsed by ARDS net, is limiting the tidal volume and plateau airway pressure to 6 ml per kg of predicted body weight and 30 cmH 2 O. Baby lung volume in ARDS is variable with severity of disease, worse is the ARDS, smaller is the baby lung. As baby lung has normal compliance, setting tidal volume according to predicted body weight, may be safe to unsafe depending upon baby lung volume. Lung behaves like viscoelastic material, which makes pulmonary mechanics time dependent. For a constant tid