CO₂ rebreathing is when a baby's exhaled breath becomes trapped in bedding and is breathed back in, rather than clearing away naturally. It's one of the reasons INPAA recommends using a mattress protector.
HushDry™ builds that protection into the fitted sheet itself. Independent testing to CO₂ rebreathing standards shows the HushDry™ layer helps reduce the risk by stopping exhaled breath being absorbed into the mattress, so it clears from the surface with normal room airflow. The deep fitted sides help too, holding the sheet snug so there are no loose layers for air to sit in.
Always remember to follow the safer sleep basics: a firm flat mattress, baby on their back, snugly fitted bedding, and no loose layers.