A back support for a chair comprising: a back support frame including a central support structure having lateral edges and a base for mounting to a chair frame and wherein the back support frame includes a plurality of flexible and spaced support arms extending laterally outward in opposing directions from the lateral edges of the central support structure, a first set of the support arms extending in a first direction and a second set of the support arms extending in a second direction, the support arms each having a peripheral edge; a one-piece, molded flexible thermoplastic material suspended in tension between the peripheral edges of the first and second sets of support arms, wherein the support arms are in a flexed, tensioned condition, the flexible material including spaced horizontal tensioning support members and spaced vertical tensioning support members that together form a flexible suspension mesh, the suspension mesh including a rear surface facing the back support frame and a front surface opposite the rear surface, wherein the suspension mesh includes a flexible periphery that defines a retaining channel molded integrally with the suspension mesh, the peripheral edges of the support arms extending into the retaining channel to retain the suspension mesh in suspension on the back support frame, wherein the horizontal and vertical support members (40, 42) and retaining channel are integrally formed as a single component, characterised in that the retaining channel includes a plurality of dividers that separate the peripheral edges of at least some of the support arms from one another, the dividers spaced apart from the peripheral edges of the support arms such that the peripheral edges of the support arms can twist independently within the retaining channel. a back support frame including a central support structure having lateral edges and a base for mounting to a chair frame and wherein the back support frame includes a plurality of flexible and spaced support arms extending laterally outward in opposing directions from the lateral edges of the central support structure, a first set of the support arms extending in a first direction and a second set of the support arms extending in a second direction, the support arms each having a peripheral edge; a one-piece, molded flexible thermoplastic material suspended in tension between the peripheral edges of the first and second sets of support arms, wherein the support arms are in a flexed, tensioned condition, the flexible material including spaced horizontal tensioning support members and spaced vertical tensioning support members that together form a flexible suspension mesh, the suspension mesh including a rear surface facing the back support frame and a front surface opposite the rear surface, wherein the suspension mesh includes a flexible periphery that defines a retaining channel molded integrally with the suspension mesh, the peripheral edges of the support arms extending into the retaining channel to retain the suspension mesh in suspension on the back support frame, wherein the horizontal and vertical support members (40, 42) and retaining channel are integrally formed as a single component, characterised in that the retaining channel includes a plurality of dividers that separate the peripheral edges of at least some of the support arms from one another, the dividers spaced apart from the peripheral edges of the support arms such that the peripheral edges of the support arms can twist independently within the retaining channel.