Large or small backpack? We say both! Rambler is a backpack which holds 22 liters which quickly can be widened so it holds 44 liters, or twice the size. Thus you can have a compact backpack for class, but at the same time a large backpack for the gym.
Except the expanding, Rambler has various side pockets, front pockets for a tablet or a 13" laptop, plus inside pocket with space for a laptop up to 17". The backpack I completely waterproof and supported by an internal frame in carbon fiber. All zippers are sealed to withstand water.
Take a look at Mission Workshops Vandal for a bigger variant of the same backpack.
Made in the USA of thick 1000d nylon with liner in waterproof membrane. Lifetime guarantee.