Abstract: Tobacco is treated to cause its expansion by a process which comprises the steps of subjecting it, in a treatment chamber, to a reduced pressure of not greater than 7 kPa, impregnating the cell structure of the tobacco with isopentane vapour at a temperature in the range of from 70.degree. C. to 100.degree. C. and maintaining the tobacco in contact with the vapour at a pressure of at least 400 kPa, removing excess isopentane vapour from the treatment chamber, contacting the impregnated tobacco with steam to expand the tobacco cell structure, reducing the pressure in the treatment chamber at a rate of at lest 10 kPa/minute, preferably 30 kPa/minute, and then venting the treatment chamber back to atmospheric pressure. The final filling value of the tobacco treated according to this process is directly proportional to the rate at which the pressure in the treatment chamber is reduced following the steam treatment of the tobacco.