PURPOSE: To adapt strings for a membrane surface by joining each string of a string layer consisting of mutually parallel spaced materials to each surface so as to be obliquely to a longitudinal extension of the membrane surface and arranging each string so as to intersect the surface with each string and abut one another.

CONSTITUTION: The layers of the strings 22 of the mutually parallel spaced materials is formed on the outside surface of a membrane layer 12 of a membrane material 10. Next, the surfaces 24 of the strings 22 are suitably joined to the membrane layer 12 extending over the entire length of the strings 22, thereby generating a closely connected part 20 between the layer 12 and the strings. The strings 22 and the layer 12 move together or the elasticity of the material itself utilized even if a slight motion occurs during the working so that the string 22 and the layer 12 are not worn out when mutually rubbed. Thus, the spaced materials can be well adapted for the membrane surface 14.