The term 'backpack material' can refer to two materials commonly used in the construction of backpacks: DENIM and NYLON. DENIM is a sturdy cotton fabric, usually dyed blue, that is often used for clothing and other items such as backpacks. NYLON is a synthetic fabric that is lightweight and durable, making it an ideal choice for backpacks. Both materials are strong and long-lasting, making them popular choices for backpack construction.