Pulmonary edema is excessive liquid accumulation in the alveolar air spaces and interstitium. This reduces gas exchange leading to increased morbidity and mortality. Clearance of pulmonary edema fluid relies on reabsorption into the alveolar interstitium and then either to the alveolar capillaries or to the lung lymphatics. How it reaches the lymphatics has been a puzzle since 1896. Our 2D model of an interstitial strip resolves that puzzle. We also show that alveolar interstitial pressures diff