Replacement Liner for the AF Mask with replaceable liner.
It is the new style (Chin-only liner).

Attaches with velcro.

Measure your head using a soft tape measure. Lay the tape measure underneath your chin, up one side of the head at the ear, over the top of the head, down the other side of the head at the ear, and ending back at your chin. Keep the tape measure fairly firm for an accurate measure.

Masks should fit snugly in the beginning. They are slightly adjustable by squeezing the sides for a taller fit or the top and bottom for a wider fit. A mask fits if it moves with your head as you turn left and right. It is too loose if you can turn your head significantly in either direction without the mask itself moving.

Small: Up to 23.5"
Medium: 24" - 26"
Large: 26.5" and Up