Backpack comprising an outer enclosure separate from the main pocket

A backpack comprising at least one shoulder strap intended for carrying the backpack by a user, the backpack comprising:

• a main pocket formed from a flexible material, connected to said at least one shoulder strap and comprising a reinforcement, said main pocket comprising an inner surface internally delimiting a first compartment located on the side opposite said at least one shoulder strap with respect to the reinforcement;
• an outer enclosure formed from a flexible material and constituting a piece separate from the main pocket, the outer enclosure comprising an inner surface;
• and
• a fastening system configured such that the backpack may occupy a separation configuration in which the outer enclosure is completely separated from the main pocket and a fastening configuration in which the reinforcement is secured to all or part of an outline of the outer enclosure,
• the inner surface of the outer enclosure and the outer surface of the main pocket internally delimiting therebetween, when the backpack is in the fastening configuration, a second compartment separate from the first compartment, the second compartment being arranged on the side opposite the reinforcement with respect to the first compartment;
• wherein the outer enclosure comprises an opening system configured to provide reversibly, in the fastening configuration, a passage through the outer enclosure giving access to the second compartment from outside the backpack.