Single limb circuit divided by a flexible septum Effectively transfers heat from the expiratory to the inspiratory side of the circuit Increased thermal efficiency rates during surgery keeps gases warm and body temperature normothermic Less weight means less torque on the ET tube and less plastic waste Decreased compliance helps lead to accurate delivered volume Limb-O circuit services patients from pediatric to adult Configurations with face masks, filters, heat moisture exchanger with filter (HMEFs) and gas sampling lines