PARI LC Plus Expiratory Filter Pads – NOT COMPRESSOR FILTERS. Expiratory filter pads work with in the expiratory filter set to help reduce the external medication deposition. This is especially important for use in enclosed spaces and with certain medications. Each pad offers one use. Be sure to talk to your physician or respiratory care specialist about the use of an expiratory filter pad. Meant only for use with a PARI's LC nebulizer equipped with an expiratory filter set.