Customized POREX® Inhaler Filters are used in metered dose inhalers to deliver measured amounts of pharmaceutical agents to patients via oral-bronchial administration. The replacement air is filtered into the device during dosage administration and the filter protects the pharmaceutical agent from contamination by airborne microbes. These filters are optimized for pore size, airflow, and dimensional tolerances based on device requirements and specifications and are designed for the most demanding production requirements. In some inhalers, the filters are also used to protect the device's mechanical valves from particles of dry powder. They can be customized to promote preservative-free packaging.