A heterogeneous-structure facial mask for thermal and humidity regulation in cold environments

Wearing a mask can help prevent respiratory diseases. However, it remains challenging to simultaneously keep the face warm and humid while ensuring sufficient oxygen intake. Forced convective airflow during respiration reduces the heat exchange efficiency of current wearable masks, especially in cold environments. Here, we present MetaMask, a heterogeneous-structure mask that employs a synergistic strategy combining asymmetric radiation control with condensation-evaporation. MetaMask recovers 82.1  ±  0.7% of heat and 94.1  ±  1.1% of moisture from exhaled air to warm and humidify the inhaled air. In a - 20 °C environment, it raises the inhaled air temperature to 26.2 °C while maintaining adequate oxygen intake. MetaMask also provides anti-frost and UV protection. This design offers an effective solution for facial protection in extremely cold conditions.