How big is the field zipper suitable for backpacks?

About 50-70 liters. Because zippers in the wild need to be packed with many necessities, such as sleeping bags, backpacks, clothes, tents, medical kits, toilet paper, rain gear, snacks, drinking water and so on. A backpack of about 50-70 liters can support long-term travel and hiking in four seasons, which can provide convenience for people's travel and can fully accommodate necessities. However, you need to choose the size of your backpack according to your actual situation, such as the purpose and time of your trip.