Manufacture of a flexible container

Method for the manufacture of a heavy-duty flexible container comprising:

• providing a first layer of flexible vulcanizable polymeric material;
• applying mask means to an inner zone of a first surface of said first layer, said mask means comprising at least one layer of continuous solid material and being arranged spaced from edges of the first layer thereby to define a substantially continuous peripheral boundary zone;
• providing a second layer of flexible vulcanizable polymeric material;
• arranging said second layer to lie adjacent said first layer so as to form an assembly comprised of both layers with the mask means sandwiched therebetween, said mask means a) preventing confronting surfaces of the first and second layers from coming into contact inwards of the boundary zone, and b) not adhering to the confronting surface materials of either the first or second layers;
• and
• subjecting the assembly to a treatment operation comprising the application of heat and pressure thereby to vulcanize said vulcanizable material and to form a vulcanized joint between said boundary zone and confronting surface region of the second layer, wherein said mask means comprise two layers of material which do not adhere to one another when subject to the temperature and pressure of said vulcanization.