This depends largely on the conditions of where and when the baby is resting: if the room and/or weather is warm, dressing the baby only in a diaper underneath their swaddle is encouraged to avoid overheating. If it’s cold out, a onesie of some kind is recommended to wear underneath the baby swaddle. Getting a transition swaddle with removable sleeves can also help keep the baby at the right temperature while sleeping, which is why the 2-in-1 Swaddle Transition Double Zipper Sleepsuit from Baby Brezza is an excellent investment for parents and babies alike.