Abstract: A method of manufacturing hollow pieces comprising the steps of forming a blank of single sheets each having a layer of gluing substance applied thereto; placing the blank onto an appropriate mandrel and subjecting it to a preliminary compression so as to impart to the blank a stiffness and to shape it into an unclosed profile as required for subsequent steps. Then the blank ends are brought together so as to define a cavity accommodating an elastic bag. The resulting blank is placed into a mould, and pressure is fed into the elastic bag to perform a final pressing.The above-described method is preferably used to manufacture helicopter rotor blades of glass plastic, which have variable cross-sectional shape over their length and exhibit higher strength and longer service life as compared with metal blades.