Select your corresponding PRO SERIES air pumper model to receive the filter you need. *Comes Pre-Installed with PRO SERIES helmet air pumpers* Backup Filters are perfect for easy swapping between long races and rides! Say Goodbye to Bulky Cloth Filters. Here at LP Engineering, we use foam true dust-filters by Uni Filter. After a long day of riding: easily unclip your filter from the air pumper, pull out the foam filter, and rinse it off with water to clean out all the dust: no soap or other solution required! Which Size Do I Need? Simply choose the option that matches the model of your LP Engineering PRO SERIES Helmet Pumper. The MX4 model uses two full-sized filters while the MX2 and MX1 models use a single full-sized filter. 'MX2 / MX1' fits the following PRO SERIES models | Includes 1 Full-Sized Filter:BLR-MX1, BLR-MX2, MX2 (Gen II) 'MX4' fits the following PRO SERIES models | Includes 2 Full-Sized Filters:BLR-MX4, MX4 (Gen II)