A crop header arranged for cutting and transporting a standing crop comprising: a header frame; an elongate cutter bar arranged along a front edge of the frame; and a draper assembly mounted on the header frame rearwardly of the cutter bar such that cut crop falls onto the draper assembly for transportation longitudinally of the header; the draper assembly including a first and a second draper guide roller (30, 30A) each arranged at a respective end of the draper assembly spaced apart along the cutter bar with an axis of each guide roller arranged substantially at right angles to the cutter bar; the draper assembly including a continuous loop of flexible material arranged to be wrapped around the rollers (30, 30A) so as to define an upper run of the flexible material on top of the rollers and a lower run of the flexible material below the rollers; wherein the flexible material includes a front edge of the upper run of the flexible material arranged at a position adjacent to but spaced from the cutter bar; characterized by a sealing member extending along the cutter bar from a first end edge of the sealing member to a second end edge of the sealing member; the sealing member comprising a first portion attached to the cutter bar and a second flexible blade portion which extends rearwardly from the first portion at the cutter bar to lie over and in contact with a front edge portion of the upper run of the flexible material adjacent the front edge; wherein the sealing member including the first portion and the second flexible blade portion is an integral plastics extrusion; and wherein the sealing member has along a full length of the sealing member between the first and second end edges of the sealing member a cross-section which is constant. a header frame; an elongate cutter bar arranged along a front edge of the frame; and a draper assembly mounted on the header frame rearwardly of the cutter bar such that cut crop falls onto the draper assembly for transportation longitudinally of the header; the draper assembly including a first and a second draper guide roller (30, 30A) each arranged at a respective end of the draper assembly spaced apart along the cutter bar with an axis of each guide roller arranged substantially at right angles to the cutter bar; the draper assembly including a continuous loop of flexible material arranged to be wrapped around the rollers (30, 30A) so as to define an upper run of the flexible material on top of the rollers and a lower run of the flexible material below the rollers; wherein the flexible material includes a front edge of the upper run of the flexible material arranged at a position adjacent to but spaced from the cutter bar; characterized by a sealing member extending along the cutter bar from a first end edge of the sealing member to a second end edge of the sealing member; the sealing member comprising a first portion attached to the cutter bar and a second flexible blade portion which extends rearwardly from the first portion at the cutter bar to lie over and in contact with a front edge portion of the upper run of the flexible material adjacent the front edge; wherein the sealing member including the first portion and the second flexible blade portion is an integral plastics extrusion; and wherein the sealing member has along a full length of the sealing member between the first and second end edges of the sealing member a cross-section which is constant.