A mask assembly includes a mask interface and a headgear assembly. The mask interface includes a housing and a seal that seals around a user's nose and/or mouth in use. The headgear assembly secures the mask interface to the user's face in use. The headgear assembly can include a top strap, a rear section, and side arms. The top strap can be manually adjustable. The rear section can be temporarily expanded to allow for donning and/or doffing of the mask assembly. The side arms can be automatically adjustable.