While supplemented oxygen is necessary when flying at high altitudes, have you ever considered how breathable air is provided to the cabin? Within most commercial aircraft, air is divided equally between two ratios: recycled air and bleed air provided by the engine or auxiliary power unit (APU). Before this air can be circulated to the cabin and exposed to passengers, it must first undergo filtration to ensure quality, breathability, and comfort. As an installed feature among many fixed-wing aircraft, high-efficiency particulate air (HEPA) systems ensure circulating air is not only free from pollutants, but also help protect against dust, dirt, fibers, microbes, allergens, and more. Within this blog, we will go over the fundamentals of cabin air filters, how they are constructed, and why they serve a large role in keeping the cabin and crew safe.