Messenger backpacks commonly accommodate laptops from about 12 inches up to 16 inches, with many listings specifically noting fits for 15" and 16" laptops.
Common closures include flap closures, zip closures, and buckle closures; some designs combine a flap with a zip or add buckles for extra security.
Some listings describe water-resistant or water-repellent fabrics; at least one notes a waterproof PU (polyurethane) coating. Such protective treatments are reported to help keep gear drier in wet conditions.
Most listings recommend spot cleaning or wiping the bag clean; a few styles list hand wash as the recommended method.
Warranties vary from a 30-day limited warranty up to lifetime limited warranty, with several mid-range limited warranties commonly offered (for example, 1-year, 3-year, and 5-year).