Every baby regulates their body heat differently so please use your best judgment. If you’re unsure, we suggest that you mimic your own layers depending on the temperature of your house and nursery. Some babies sleep with light PJs underneath while others simply wear their diaper underneath the Zipadee-Zip! If your baby sleeps colder, or if you live in a colder climate, do not use a loose blanket to add warmth. Instead, we suggest either using a Fleece Zipadee-Zip or adding layers under the regular Zipadee-Zip for added coziness. Pro tip: Babies tend to sleep better in cooler temperatures so avoid the temptation to add too many layers. According to the American Academy of Pediatricians, babies do best sleeping in a room with cooler temperatures, about 68–72˚F.