Pack Liner

A pack liner is a waterproof or water-resistant bag that fits inside a backpack to protect gear from moisture and water infiltration. Typically made from lightweight materials like silnylon, plastic, or coated fabrics, pack liners serve as a backup waterproofing system even when using a pack cover or waterproof backpack. They're essential for keeping sleeping bags, extra clothing, and other critical gear dry during rain, river crossings, or in humid conditions, and can also help organize gear within the main pack compartment.