An inflatable frameless mask (10) for the ventilation of patients comprising: - a flexible and inextensible shell (20) provided with a peripheral edge (23) generally closed in a loop able to come in forced, fluid-tight contact with the face of the patient and to inscribe at least the nose of the patient, - means (40) for injecting a breathable gas positioned on the shell (20) for the injection of breathable gas inside a volume enclosed between the shell (20) and the face of the patient； - means (50) for the outflow of gases exhaled by the patient for the exit from the volume of the gases exhaled by the patient； - wherein the breathable gas introduced into the closed volume by the injection means (40) inflates the shell (20) from a deflated configuration of the shell (20) to an inflated configuration of the shell (20), wherein in the inflated configuration the breathable gas inside the closed volume is at a higher pressure than ambient pressure； and - wherein at least one portion of the flexible shell (20) is optically transparent.
