When evaluating sleeping bags, focus on the Temperature Rating (Comfort, Limit, and Extreme), which must be tested according to EN 13537 or ISO 23537 standards. Pay close attention to the Fill Material: Down (measured by Fill Power) offers the best warmth-to-weight ratio, while Synthetic (Polyester/Hollow Fiber) is more cost-effective and performs better in damp conditions. Additionally, verify the Shell Fabric durability, typically measured in Denier (e.g., 20D to 40D Ripstop Nylon), and ensure the use of high-quality YKK zippers with anti-snag features to prevent mechanical failure in the field.