Respiratory mask comprising a headgear comprising several flexible straps (21a-21d), wherein at least one of said flexible straps (21a-21d): - comprises an elongated main body comprising a core region terminated by a free end with a tip, an outer face located externally, and detachable securing means (24A, 24B) arranged on said outer face, - is configured for being foldable so that, when folded, the free end of said flexible strap (21a-21d) can be positioned by a user in several different positions located along the outer face of said at least one flexible strap (21a-21d) and removably secured in one of said several different positions by means of the detachable securing means (24A, 24B), - and further comprises several markings arranged on the outer face of said at least one flexible strap (21a-21d), said several markings corresponding to different tightenings of said at least one flexible strap (21a-21d), wherein: - the markings comprise several increasing numbers, and - when said at least one flexible strap (21a-21d) of the headgear is folded, the tip of the free end of said at least one flexible strap (21a-21d) is positioned vis-à-vis one given marking of said several markings so as to designate said given marking thereby assisting the user in choosing a desired tightening of said at least one flexible strap (21a-21d), characterized in that: - the detachable securing means (24A, 24B) of the headgear comprise a little-loop region comprising a multitude of little loops and a little-hook region comprising a multitude of little hooks cooperating together for ensuring a desired removable attachment of the little-hook region to the little-loop region, - the core region of said at least one flexible strap (21a-21d) of the the headgear comprises the little-loop region and the free end comprises the little-hook region, and - the markings are arranged in the little-loops region of the elongated main body of at least one flexible strap (21a-21d) of the the headgear, and wherein: - the little-hook region arranged on the elongated main body is configured for being attached to the little-loop region arranged on the free end of said at least one flexible strap (21a-21d), when said free end is folded over the core region of said elongated main body, thereby forming a fixation loop, and - when folded, the free end of one or several flexible straps (21a-21d) of the headgear is maintained along and in contact with the outer face of said at least one flexible strap (21a-21d) by means of the detachable securing means (24A, 24B), in a desired position wherein the tip of the free end of said one or several flexible straps (21a-21d) designates said one given marking of the several markings. - comprises an elongated main body comprising a core region terminated by a free end with a tip, an outer face located externally, and detachable securing means (24A, 24B) arranged on said outer face, - is configured for being foldable so that, when folded, the free end of said flexible strap (21a-21d) can be positioned by a user in several different positions located along the outer face of said at least one flexible strap (21a-21d) and removably secured in one of said several different positions by means of the detachable securing means (24A, 24B), - and further comprises several markings arranged on the outer face of said at least one flexible strap (21a-21d), said several markings corresponding to different tightenings of said at least one flexible strap (21a-21d), - the markings comprise several increasing numbers, and - when said at least one flexible strap (21a-21d) of the headgear is folded, the tip of the free end of said at least one flexible strap (21a-21d) is positioned vis-à-vis one given marking of said several markings so as to designate said given marking thereby assisting the user in choosing a desired tightening of said at least one flexible strap (21a-21d), - the detachable securing means (24A, 24B) of the headgear comprise a little-loop region comprising a multitude of little loops and a little-hook region comprising a multitude of little hooks cooperating together for ensuring a desired removable attachment of the little-hook region to the little-loop region, - the core region of said at least one flexible strap (21a-21d) of the the headgear comprises the little-loop region and the free end comprises the little-hook region, and - the markings are arranged in the little-loops region of the elongated main body of at least one flexible strap (21a-21d) of the the headgear, - the little-hook region arranged on the elongated main body is configured for being attached to the little-loop region arranged on the free end of said at least one flexible strap (21a-21d), when said free end is folded over the core region of said elongated main body, thereby forming a fixation loop, and - when folded, the free end of one or several flexible straps (21a-21d) of the headgear is maintained along and in contact with the outer face of said at least one flexible strap (21a-21d) by means of the detachable securing means (24A, 24B), in a desired position wherein the tip of the free end of said one or several flexible straps (21a-21d) designates said one given marking of the several markings.