Contrary to thermo-plastic for EVA, the minimum closing power must be
maintained until the moment of opening the mould in as much the
pressure developed in the cavities during the cross-linking and
cooking steps must be opposed. Opening of the press must be very fast
in order to prevent the manufactured article from deformation or
pinched by the mould during the expanding phase, which is extremely
rapid. For these reasons the hydroblock systems are limited.