A pillow for a patient interface structure configured to deliver a flow of breathable gas to a patient, comprising a neck portion defining a passage configured to receive the flow of breathable gas. A generally conical portion extends from the neck portion and comprises an orifice configured to deliver the flow of breathable gas to the patient. Furthermore, the generally conical portion comprises a sealing surface configured to engage the naris of the patient, wherein a base portion of the conical portion extends from the neck portion either in unequal amounts around the neck portion and the sealing surface and the orifice are concentric with the neck portion, or in equal amounts around the neck portion and the sealing surface and the orifice are non-concentric with the neck portion.
