I have rode a bike in cold weather and it becomes uncomfortable to breath in cold air. This allows my body heat to Warm the air before entering my lungs. I also believe the resistance that results I feel is a beneficial training aid, I'll know more next spring. An attractive piece of cold weather gear.
https://www.amazon.com/Hi-crazystore-Respirator-Filtered-Activated-Filtration/dp/B072Q3W4W6