Abstract: A unilimb breathing circuit has a proximal end coupling member, a distal end coupling member, an expiratory tube extending between the proximal and distal end coupling members, and an inspiratory tube extending between the proximal and distal end coupling members. The expiratory tube is a corrugated expiratory tube that is expandable between a fully compressed rest position, and a fully expanded rest position, and has a plurality of intermediate rest positions. At the plurality of intermediate rest positions, the expiratory tube is capable of maintaining its rest length without the exertion of an external force. The inspiratory tube is a corrugated inspiratory tube having a length that is variable between a fully compressed rest position and a fully expanded rest position, and includes a plurality of intermediate rest positions between the fully expanded rest position and the fully compressed rest position.