Not sure if you should opt for size S or size M?
The answer is in the next few lines.
The difference between size S and size M is in the chin strap which will be narrower (size S).
Although size M is suitable for all adults, some of them have a fairly thin face, which is why we recommend size S.
To find out what size you need, we invite you to measure
the distance between your lobe and the middle of your chin:
• If the distance is less than or equal to 12 cm, we recommend that you choose the size S.
• If the distance is greater than 12 cm, we recommend that you choose size M.