STM Trilogy Carrying Case (Backpack) for 38.1 cm (15") Notebook - Granite Gray - Impact Resistant Interior, Moisture Resistant Exterior, Water Resistant Exterior, Dirt Resistant - Polyurethane, Polyster Body - Handle, Shoulder Strap - 459.7 mm Height x 289.6 mm Width x 149.9 mm Depth Omne trium perfectum. It's said that good things come in threes, so it's no surprise you'll discover plenty of great stuff in our aptly named Trilogy backpack. From a trio of storage compartments (two main ones, plus a full-size front pocket) to a triad of additional pockets (internal mesh, external drop, overflow stash) and much, much, much more. Designed to fit your lifestyle, we consider it a triumph of functionality and style.