This medium size backpack has plenty of room with a big inner pocket, separate section for a 15'' laptop, front pocket, and a hidden pocket at the back for valuables. The bag is made out of a water-resistant material. 
100% polyester
Fabric weight: 9.56 oz/yd² (325 g/m²), weight may vary by 5%
Dimensions: H 16⅞" (42cm), W 12¼" (31cm), D 3⅞" (10cm)
Capacity: 4 gallons (15l)
Maximum weight limit: 44lbs (20kg)
Water-resistant material
Large inside pocket with a separate compartment for a 15” laptop, front pocket with a zipper, and a hidden pocket with zipper on the back of the bag
Top zipper has 2 sliders with zipper pullers
Silky lining, piped inside hems, and a soft mesh back
Padded ergonomic bag straps from polyester with plastic strap regulators