For new parents, the zipper design of a baby's sleep sack is an easily overlooked yet crucial detail. Especially during frequent nighttime diaper changes, the zipper's position and opening/closing method directly affect the baby's warmth retention and sleep quality. This article compares the pros and cons of front-zip and side-zip sleep sacks from multiple dimensions, including structural features, diaper-changing convenience, warmth retention, and safety. Combining pediatric experts' advice and real-user feedback, it provides a scientific purchasing guide to help reduce the risk of babies catching cold at night while improving the parent-child sleep experience.