Median palatal suture is a relief area while making upper edentulous impression because:

Maxilla Supporting structures Hard palate—rugae Residual alveolar ridge—maxillary tuberosity Limiting structures  Labial frenum Labial vestibule Buccal frenum Buccal vestibule Hamular notch Fovea palatine Posterior palatal seal area Relief area: Midpalatine suture Incisive papilla Torus palatinus Stress-bearing areas Primary Horizontal slopes of hard palate lateral to Median sutures Secondary Crest of the residual alveolar ridge Rugae Maxillary tuberosity