Expiratory limb for a breathing circuit

A breathing circuit component comprising:

• a patient end for connecting to a patient interface component,
• a gases-source end comprising a gases-source end connector configured for receiving inspiratory gases and for delivering a bulk flow of expired gases thereto;
• an outer conduit, insufficiently sturdy to be self-supporting, extending from the patient end to the gases-source end;
• lateral reinforcement configured to support the outer conduit and reinforce the outer conduit against contraction;
• longitudinal reinforcement, distinct from the lateral reinforcement, configured to support the outer conduit and reinforce the outer conduit against stretching, and
• an inner conduit continuously extending within said outer conduit from the patient end to the gases-source end, thereby completely dividing said breathing circuit component into
• an inner gases passageway, within said inner conduit, configured to carry the inspiratory gases from the gases-source end connector to a patient and
• an outer gases passageway, between said inner conduit and said outer conduit, configured to carry the bulk flow of the expired gases from the patient to the gases-source end connector, the complete division of the outer gases passageway from the inner gases passageway configured to reduce the possibility of rebreathing expiratory gases by the patient during use,
• wherein substantially all of said outer conduit comprises a material that allows the passage of water vapor from said outer gases passageway to ambient air without allowing the passage of liquid water or the bulk flow of the expired gases, such that the outer conduit reduces relative saturation in the bulk flow of the expired gases to reduce rain out along the outer conduit when in use.