Chafing is one of the most painful things that a runner can deal with, and backpacks are one of the most common items a runner wears that create this problem. A good fit is the best way to stop chafing from occurring since repetitive rubbing is what causes it to happen. Stopping your backpack from making direct contact with your skin also prevents chafing. Unfortunately, this means avoiding running without a shirt, which can be uncomfortable on hot days. Keeping the skin on your back safe is worth a little extra sweat though.