Fitpacks are the only way to ensure that you'll have the right size when ordering a brand new mask. These packs are designed for convenience and have multiple size cushions or pillows in the pack. They are ideal for people that can't get in to a store for a mask fitting. Simply find the right size once you receive the mask and discard the ones you don't need. FitPacks are more expensive that single mask sizes because they cost more to produce.