When silicone rubber-impregnated and/or coated fabric pieces are mated, with their treated surfaces inside, and joined along a periphery to form a bag, a silicone rubber composition having a tris(trialkoxysilylalkyl) isocyanurate blended as an adhesion promoter is used as a sealer where the peripheral portions of the fabric pieces are joined together whereby an improved bond is established therebetween.