Professional Universal Replacement Standard Filter Cotton for ResMed CPAP S9/S10 Dust Filters Features: Ultra-fine PM2.5 dust filters,filter fine dust particles. It is recommended to replace 1-2pcs within a month. Specifications: Material: Cotton Size: 5.3 X 3.5 cm/2.09 X 1.38" Application: Professional for ResMed CPAP S9/S10 Notes: 1. Due to the different monitor and light effect, the actual color of the item might be slightly different from the color showed on the pictures. Thank you! 2. Please allow 1-3cm measuring deviation due to manual measurement. Included: 1 X Filter Cotton