Our backpacks come in different capacities and sizes. Different capacities and sizes are suitable for different scenarios. 1.If you need to do a short trip within one day, we recommend backpacks or backpack sets below 40L. 2. If you need to do outdoor activities within three days, we recommend backpacks or backpack sets within 40L-60L (some of the 40L-60L backpack sets are equipped with a Molle Pouch, which can take up the extra storage task for you). 3. If you have more than 5 days of outdoor activities planned, a 60L or even 70L backpack or backpack set will be more suitable. 4. If you are traveling under tougher conditions than usual, the higher quality Cordura products will be the best choice.