There are five different models which allow different volumes of airflow. This is a pack of 2 racing filters.
Race Filters: Highest airflow, lowest resistance and least warming for high-intensity activity. Race 1 is the highest resistance and warming of the race filters, Race 2 is mid-range, Race 3 is the least resistance/highest airflow.
Sport Filter: Medium airflow and resistance, warms air significantly and is used for light- to moderate-intensity exercise.
Asthma Filter: Lowest airflow and highest heat recovery. For those with Asthma, or for use in cold temperatures at low intensity levels.
Filters should be dried completely after each use. With adequate care, each filter should last for 20-30+ sessions. Airtrim Mask comes with the sport filter installed and a spare asthma filter.
Also available: Race Filter Pack (1 of each Racing 1,2,3), Sport Filters, Asthma Filters