[ DIMENSIONS OF PET BACKPACK ]: To ensure a comfortable fit, measure your dog's sitting height (from front legs to the top of the head) before purchasing. If the sitting height is outside the recommended range, the backpack may be unsuitable. Sizes: - L size: 17.4 x 13.4 x 10.6 in, ideal for cats under 15.4 lbs and dogs up to 13 lbs with sitting height ≤15.6 in. - XL size: 19.3 x 15.7 x 12.9 in, suitable for cats weighing 15.4-24 lbs and dogs 13-22 lbs with sitting height between 15.6 in and 17.6 in. [ EXPANDABLE DESIGN ]: The expanded size is 13.4 in L x 24.4 in W x 17.3 in H. This unique design allows for extra space, enhancing your pet's comfort and promoting better air circulation, which helps to alleviate travel anxiety. [ GREAT VENTILATION & COMFORT ]: Features 4 breathable mesh windows that ensure optimal airflow, allowing you to easily check on your pet while they enjoy the view. The carrier is designed for easy entry and exit, and includes a comfortable pet cushion with a removable, washable cover for hygiene. [ ERGONOMIC DESIGN ]: The padded and widened shoulder straps and back panel deliver support and comfort. Two retractable buckles secure the straps, ensuring stability and preventing slippage during use. [ SAFETY & STORAGE ]: Constructed from high-quality, waterproof Oxford Cloth that is scratch-resistant and pet-safe. Equipped with lock-type zippers to prevent accidental openings and a built-in retractable leash to keep pets secure. Additionally, side pockets provide convenient storage for food, waste bags, or essential accessories. Practical use scenarios include going on hikes, traveling on public transport, or simply enjoying a day out in the park, ensuring a comfortable and secure experience for both you and your pet.