In an installation comprising a chain of rods from which woven material in strip form is suspended in folds, the discharge of hot air or steam through a blowing nozzle is subjected to the cyclic action of a regulating device for progressively reducing the nozzle discharge from a predetermined maximum value during commencement of formation of a fold to a zero value after only a fraction of the time required for complete formation has elapsed. The installation is primarily intended for use in steaming machines.