Similar in function to backpacks, messenger bags ensure comfort for people carrying heavy and/or bulky items, while allowing easy access to the contents.
A true messenger bag includes a second, thinner, stabilising strap that is fastened either around the rider's waist or diagonally across the chest.
Compared to a backpack, it is easier to place and remove text-books, notebooks and supplies from a messenger bag because they can be easily shifted to the side of the body, providing better accessibility.
Contemporary bags use thicker gauges of waxed canvas and tarp shielding for the inner waterproof lining.
Some companies eschew the standard PVC waterproof lining for compounds such as thermoplastic polyurethanes, which are more expensive, more durable, more environmentally friendly, and less volatile.