Investigations of infants dying unexpectedly have reported up to 28% being found completely under bedding. No detailed physiological studies looking at the possibilities of asphyxia in this situation are available. The aim was to determine the potential for asphyxia under different types and thicknesses of bedding. A mechanical model of a 3-month-old infant's respiratory system was used. Bedding was positioned over the head in a supine position, and inspired carbon dioxide recorded. With a fixed respiratory rate and tidal volume, carbon dioxide accumulation increased with increasing layers of blankets. Up to 8.3% inspired carbon dioxide was recorded with more than four layers of blankets. A cotton sheet between the face and blankets reduced the accumulation by half. An infant found dead under bedding may have been exposed to an asphyxial stress. Suffocation from rebreathing trapped, expired gases can be a cause of death in this situation.