The important thing to keep in mind is that airflow generally follows the path of least resistance. Instead of using more energy to get through an obstacle, air will try to find and easier route around it. Now when it comes to face masks, filtration and breathability are sort of at opposite ends of the spectrum. A better filter is just inherently more resistant to airflow. So when you’ve got a mask that only prioritizes filtration over breathability, you can actually end up with a less effective mask.