Measure nose to chin
Use a piece of string or a ruler to measure the distance between the tip of your nose and the point of your chin. Make sure not to measure under the chin as the B2 Mask is not designed to wrap below the chin.
Ensure that your nose to chin measurement is within the range shown on the table above. The bottom strap of the B2 Overlay, which fastens around the back of the neck, has a maximum circumference of 21 inches (53 cm).
Compact FitB2 Mask has a flexible facepiece that conforms to your face to form a seal. It is normal to take a few days of use for the facepiece to break in and achieve the best position for sealing.
Adjustment and Seal
The B2 Mask is designed to sit low on the bridge of your nose. If you have a prominent or low nose bridge, you can flip the inner seal up achieve a tighter fit.