The longest-running knock against memory foam mattresses is their tendency to trap body heat and sleep hot. However, innovations such as infusing semi-liquid gel beds into the foam can improve airflow and breathability. Not everyone enjoys the hug sensation of contouring memory foam either, saying that they sink too far into the surface and feel trapped. Also, memory foam's chemical properties can be an irritant for people with asthma, allergies, and other breathing problems.