Jansport backpacks are made of a variety of materials, including durable polyester fabric and nylon. Many have leather-reinforced bottoms. Any backpack, even if you use it gently, needs to be cleaned occasionally. Dirt and debris from the environment make them look soiled over time.
Open all the compartments on the backpack. Remove all the contents and then turn it upside down. Shake it out to remove any debris. Place the backpack on a towel.
Brush off dust and dry grime with the lint brush. You can also use a hand vacuum.
Fill a bucket with water. Dampen a cloth rub it over dirty areas. Jansport.com advises against using anything other than a cloth and plain water (no matter what type of material). Don't use detergent or bleach or machine wash them.
Hang the backpack up to dry. Keep all the compartments open to speed up this process.