Abstract: A seam between a pair of porous layers of sheet material includes a bead of cured nitrile latex material disposed on one side of one of the layers and extending transversely through the pores of both layers. The same is produced in its preferred form by first tensioning the juxtaposed layers, which are then clamped between a knife edge and a backup plate to define at least one lateral limit of the seam where the porosity is thus temporarily eliminated, after which liquid nitrile latex material is passed under pressure along the knife edge and toward the backup plate. The first layer filters out any latex film or cured particles or air bubbles which thus do not impair the integrity of the seam. The latex is then cured, and if desired, the sheet material is trimmed away at one side of the seam.