Hydrophobic wrapper

1. A smoking article comprising:

a tobacco substrate comprising at least 15% by weight humectant; and

a paper wrapper disposed about the tobacco substrate and comprising an inner surface in contact with the tobacco substrate and an outer surface,

wherein the paper wrapper comprises at least one hydrophobic surface due to hydrophobic groups comprising fatty acid esters covalently bonded to cellulosic material of the paper,

wherein the hydrophobic surface is formed by at least 100 discrete hydrophobic islands disposed throughout at least a downstream-most 75% portion of the paper wrapper, and

wherein the at least one hydrophobic surface comprises the inner surface, the outer surface, or both; the plurality of discrete hydrophobic islands are not present in the most upstream 25% portion of the paper wrapper.

2. A smoking article according to claim 1 , wherein the paper wrapper maintains the tobacco substrate in cylindrical form and the tobacco substrate comprises at least 20% by weight humectant.

3. A smoking article according to claim 1 , wherein the paper wrapper has a water contact angle of at least about 100 degrees.

4. A smoking article according to claim 3 , wherein the paper wrapper has a basis weight in a range from about 20 to about 50 grams per square meter and a hydrophobic reagent used to provide the hydrophobic groups has a basis weight in a range from about 0.1 to about 3 grams per square meter.

5. A smoking article according to claim 1 , wherein the fatty acid esters are covalently bonded to cellulosic material of the paper by reacting in situ a fatty acid chloride with the cellulosic material.

6. A smoking article according to claim 5 , wherein the fatty acid chloride is palmitoyl chloride, stearoyl chloride, behenoyl chloride, or a mixture of palmitoyl chloride and stearoyl chloride.

7. A smoking article according to claim 1 , wherein the wrapper exhibits a Cobb measurement value (60 s) of less than 20 g/m 2 .

8. A smoking article according to claim 1 , wherein the hydrophobic paper is produced by a process comprising the steps of: applying a liquid composition comprising a fatty acid halide to at least one surface of a paper, maintaining the surface at a temperature of about 120° C. to about 180° C., wherein the fatty acid halide reacts in situ with protogenic groups of material in the paper resulting in the formation of fatty acid esters.

9. A smoking article according to claim 8 , wherein the process comprises applying a liquid composition comprising stearoyl chloride or palmitoyl chloride to at least one surface of a paper at a temperature of about 120° C. to about 180° C., wherein hydroxyl groups in the cellulosic material of the paper reacts in situ with the stearoyl chloride or palmitoyl chloride.

10. A smoking article according to claim 9 , wherein the process comprises applying the liquid composition to the at least one surface of a paper at a rate of in a range from about 0.1 to about 3 grams per square meter to render the at least one surface of the paper hydrophobic.

11. A smoking article according to claim 8 , wherein the process comprises applying the liquid composition to the at least one surface of a paper at a rate of in a range from about 0.1 to about 3 grams per square meter to render the at least one surface of the paper hydrophobic.

12. An aerosol-generating system comprising:

an aerosol-generating device comprising a heating element; and

an aerosol-generating smoking article according to claim 1 ;

wherein the aerosol-generating device is configured to releasably receive the aerosol-generating smoking article and the heating element provides heat to the aerosol-forming substrate of a heated smoking article.

13. A smoking article according to claim 1 , wherein the paper wrapper has a basis weight in a range from about 20 to about 50 grams per square meter and a hydrophobic reagent used to provide the hydrophobic groups has a basis weight in a range from about 0.1 to about 3 grams per square meter.

14. The smoking article of claim 1 , wherein the paper wrapper comprises at least one hydrophobic surface due to hydrophobic treatment, and wherein the paper wrapper comprising the at least one hydrophobic surface has a permeability that is less than 10% lower than the permeability of the paper wrapper before hydrophobic treatment.

15. The smoking article of claim 1 , wherein the paper wrapper comprises a downstream end adjacent a mouth piece and an upstream end, and wherein the hydrophobic surface is present at the downstream end and is not present at the upstream end.