Separator for cylindrical cell of the outwardly guided type, wherein a sheet material is wound around a mandrel, and starting from the winding step until the insertion of a separator into the cell, an outward support is used that renders the binding of neighboring turns of the separator winding unnecessary, and the separator sheet has an extended portion, with the extension being at least equal to the radius of the separator cylinder, and with this extended portion being wetted with distilled or de-ionized water until the material softens and the winding and the mandrel are rotated and the bottom part is folded back and heat fused to close the separator cylinder.