The expansion chamber (10) comprises a main section and two openings for connecting to an assisted breathing apparatus (1) in which air is circulated with a larger inlet volume to reduce noise. It is made in one piece from a flexible material with a preferable thickness of between 0.2 and 0.3 mm, a hardness of 30 - 40 Shore, and a stretch capability of over 300 per cent to absorb vibrations caused by air passing from one opening to the other.
