Abstract: A knapsack has at least one reinforcing or stiffening element that is received in pockets provided on a back wall and that is concavely curved at least in part in the longitudinal and/or transverse directions. The stiffening element concavely deforms the back wall in the longitudinal and/or transverse directions. An elastic support band extends along a lower area of the stiffening element, and a supporting net is stretched therefrom to the upper area of the stiffening element, bridging a concavity in the stiffening element. This support band can extend between a lower marginal area of the stiffening element and the supporting net. In order to make it easier to mount and dismount the knapsack, and to ensure reliable fitting thereof, the stiffening element is a flat one-piece element, provided if necessary with openings, which when it is curved is releasably stretched in the longitudinal and transversal directions only by its upper and lower ends fitting in the upper and lower pockets in the back wall.