Hardcore Protection: Three layers of high-tech fabric create a protective barrier. Outer layer: 420D encrypted Oxford cloth + PU coating, waterproof rating of 2000mm, can withstand heavy rain and wash away stains with a single wipe. Middle layer: EPE pearl cotton cushioning layer, protects against thorns, scratches, and rock collisions, safeguarding the backpack body and internal items such as computers. Inner Layer: Breathable mesh fabric prevents moisture buildup, keeping the backpack surface dry. Smart Adaptability: Full-Size Compatible Elastic Design Size Compatibility: Contracted State: Compatible with 20-35L backpacks (drawstring closure); Expanded state: Stretches to fit 50-70L backpacks (elastic hem extension), suitable for 90% of backpack styles on the market. Breathable design: Back mesh ventilation windows prevent sweating during prolonged use, ideal for hot and humid environments like high-altitude hiking. Real-world testing: All-round protection from rainforests to deserts Rainforest hiking: Provides continuous protection for 3 hours in heavy rain, keeping the laptop and sleeping bag inside the backpack completely dry; Desert crossing: Fine sand and dust cannot penetrate, and the scratch-resistant fabric protects against cactus spines and other plant thorns; Snow mountain climbing: The coating remains flexible at -15C, maintaining excellent elasticity.