Lungs do not collapse between breaths and some air always remains in the lungs which can never be expelled because

The surface of the lungs is covered by the visceral pleura, and the portion of the sac that lines the thoracic cavity is called the parietal pleura. Cohesive forces exerted by the fluid between the two pleural membranes cause the stretchable lung to adhere to the thoracic cage. The intrapleural pressure in the fluid between the pleural membranes is normally sub atmospheric. This negative intrapleural pressure pulls the lungs always towards thoracic walls and do not allow the lungs to collapse in between breaths.