Two-way zipper for easy changes! These are the BEST sleep sacks, breathable merino wool inside with a cotton outer layer. So comfy, wish they made them for adults! Every other sleep sack out there is filled with polyester. Wash and wear SO well. No stains, pilling, or tears at all, looks new. Washed only 2-3 times as didn't start using it until baby almost too big for the size. From Woolino: With Woolino, there is no need to worry. The exceptionally breathable Merino wool naturally regulates baby's body temperature, which helps your child to sleep safely and comfortably through the night. It gives you peace of mind and a good night sleep as well. This amazing baby sleeping bag also saves you buying different sleep sacs for different seasons because you can use it year-round.