To provide a sheet material that is produced by directly blowing a hot gas mainly including superheated steam via the air-permeating belt zone restraining the free shrinkage of the sheet into the moisture inside the sheet to cause the instantaneous vaporization (in a pressure flow) of the moisture whereby the sheet is made porous and disclose a method of producing the same and a drier for the foamed sheet.

A moistened sheet material 35 is nipped between the externally heated rotor 1 equipped with an outlet 19 for blowing a hot gas from the circumferential direction and the air-permeating endless fabric 36 that moves synchronously to the rotation of the rotor 1 under such a tension that can restrain the drying shrinkage of the sheet whereby the moisture in the sheet is promptly and directly vaporized and the sheet is made porous.