Abstract: A removable one-piece, puncture resistant, flexible inner liner insert for use in a variety of backpacks, soft body portfolios, carrying bags and the like. The liner insert has an adjustable variably sized bottom portion having at least four side regions, at least four stress relief joints, a front flap attached to the first side region of said bottom portion, a back flap attached to the second side region of the bottom portion, and a first side flap and a second side flap attached to the third and fourth side regions of the bottom portion respectively. Additionally, a plurality of size adjusting perforations are located adjacent each of the four joints and run inwardly, at an approximately 45° angle, towards the center of the bottom portion. The size adjusting perforations enable an individual to easily adjust the size of the bottom portion of the liner insert such that it substantially corresponds to the size of the bottom region of the back pack that the liner insert is to be installed within.