A seal member for an interface assembly, the seal member comprising a: a sidewall; and a face contacting surface that forms a flange that curls inward from the sidewall, the face contacting surface comprising an edge that at least partially defines an opening, the face contacting surface also comprising a first cheek surface and a second cheek surface, the first and second cheek surfaces being configured to contact a medial cheek surface and/or a lateral surface of a respective side of the nose of a patient, in use, characterized in that: the sidewall comprises a first thin walled portion and a second thin walled portion, the first thin walled portion being proximal to the face of the user, in use, wherein the first and second thin walled portions (142, 144) are connected with a thickened band; the face contacting surface curls inwards from the first thin walled portion of the sidewall; and a first thickened panel is positioned at or proximate a position of the flange corresponding to the first cheek surface; and a second thickened panel is positioned at or proximate a position of the flange corresponding to the second cheek surface, wherein the first and second thickened panels are locally thickened regions of the flange, each of the thickened panels having a side at or proximate to the edge. a sidewall; and a face contacting surface that forms a flange that curls inward from the sidewall, the face contacting surface comprising an edge that at least partially defines an opening, the face contacting surface also comprising a first cheek surface and a second cheek surface, the first and second cheek surfaces being configured to contact a medial cheek surface and/or a lateral surface of a respective side of the nose of a patient, in use, characterized in that: the sidewall comprises a first thin walled portion and a second thin walled portion, the first thin walled portion being proximal to the face of the user, in use, wherein the first and second thin walled portions (142, 144) are connected with a thickened band; the face contacting surface curls inwards from the first thin walled portion of the sidewall; and a first thickened panel is positioned at or proximate a position of the flange corresponding to the first cheek surface; and a second thickened panel is positioned at or proximate a position of the flange corresponding to the second cheek surface, wherein the first and second thickened panels are locally thickened regions of the flange, each of the thickened panels having a side at or proximate to the edge. the sidewall comprises a first thin walled portion and a second thin walled portion, the first thin walled portion being proximal to the face of the user, in use, wherein the first and second thin walled portions (142, 144) are connected with a thickened band; the face contacting surface curls inwards from the first thin walled portion of the sidewall; and a first thickened panel is positioned at or proximate a position of the flange corresponding to the first cheek surface; and a second thickened panel is positioned at or proximate a position of the flange corresponding to the second cheek surface, wherein the first and second thickened panels are locally thickened regions of the flange, each of the thickened panels having a side at or proximate to the edge.