resplabs CPAP Mask Liners for ResMed AirFit F40 Full Face Mask — Medium If your F40 mask leaves red marks, causes skin irritation, or leaks air during the night, a mask liner can help. These soft, reusable fabric covers sit between your skin and the mask cushion — creating a comfortable barrier that reduces pressure points and helps improve your mask seal. WHAT IS INCLUDED? 4 reusable mask liners sized for the ResMed AirFit F40 Medium cushion HOW IT WORKS: Place the liner over your existing F40 mask cushion before putting on your mask. The fabric layer absorbs facial oils and moisture while creating a softer surface against your skin. Many users notice improved comfort from the first night. COMPATIBLE MASKS: - ResMed AirFit F40 (Medium cushion) NOT COMPATIBLE: Other F40 cushion sizes, F20, F30, F30i, N20, or other mask models. We make mask-specific liners for each — check our storefront. HOW LONG DO THEY LAST? Each liner lasts approximately one month with proper care. Hand wash with mild soap, air dry, and rotate between liners. The 4-pack provides 2-4 months of use. TIP: It may take 2-3 nights to find the optimal position on your mask. Slight adjustments can make a big difference in seal quality and comfort.