A method of making a reconstituted tobacco sheet, comprising: providing tobacco stems or tobacco stalks or a mixture thereof; conditioning the tobacco stems or tobacco stalks such that their moisture content is increased to at least about 40 % Oven Volatiles determined by measuring the percentage weight loss from the stems upon drying a sample of the stem material in an oven at 100 ± 1 oC for 3 hours ± 0.5 minutes; processing the conditioned tobacco stems or tobacco stalks in a twin screw extruder to so as to obtain a pulp suspension having a Schopper-Riegler index of at least about 30 degrees and comprising tobacco stem or tobacco stalk refined fibres having an average length of at least about 200 micrometres, wherein the Schopper-Riegler index is determined as defined by the 2014 publication of ISO 5267-1; combining the pulp suspension with tobacco cast leaf material to obtain a slurry; and forming a sheet from the slurry; wherein the step of processing the conditioned stems or stalks is carried out in a twin screw extruder comprising at least a first and a second conveying sections adapted to advance the material being processed along an axial direction of the extruder and at least a kneading section adapted to restrict the flow of the material being processed along the axial direction and to exert a kneading and shearing action on the stems, wherein the at least one kneading section is located between the first and the second conveying sections; and wherein the reconstituted tobacco sheet has a tensile strength of at least about 245 Newtons per metre determined as defined by the 2014 publication of ISO 1924/2. providing tobacco stems or tobacco stalks or a mixture thereof; conditioning the tobacco stems or tobacco stalks such that their moisture content is increased to at least about 40 % Oven Volatiles determined by measuring the percentage weight loss from the stems upon drying a sample of the stem material in an oven at 100 ± 1 oC for 3 hours ± 0.5 minutes; processing the conditioned tobacco stems or tobacco stalks in a twin screw extruder to so as to obtain a pulp suspension having a Schopper-Riegler index of at least about 30 degrees and comprising tobacco stem or tobacco stalk refined fibres having an average length of at least about 200 micrometres, wherein the Schopper-Riegler index is determined as defined by the 2014 publication of ISO 5267-1; combining the pulp suspension with tobacco cast leaf material to obtain a slurry; and forming a sheet from the slurry; wherein the step of processing the conditioned stems or stalks is carried out in a twin screw extruder comprising at least a first and a second conveying sections adapted to advance the material being processed along an axial direction of the extruder and at least a kneading section adapted to restrict the flow of the material being processed along the axial direction and to exert a kneading and shearing action on the stems, wherein the at least one kneading section is located between the first and the second conveying sections; and wherein the reconstituted tobacco sheet has a tensile strength of at least about 245 Newtons per metre determined as defined by the 2014 publication of ISO 1924/2.