A press bobbin for yarn treatment formed of a cylindrical wall which is fabricated by blow molding of a synthetic plastic and comprises relatively thin-gage zones and relatively thick-gage zones extending circumferentially and alternately arranged in the axial direction of the bobbin. The cylindrical wall defines an indentation configuration along the axial direction wherein the thin-gage zones correspond to projecting portions and the thick-gage zones to recessed portions. The thick-gage zones are defined with holes for passage of liquid and the thin-gage zones are, when pressed axially, bendable in a U-form to protrude outwardly, thereby to be axially compressible. The relatively thick-gage zones may be provided with reinforcing members which serve to suppress compression of the bobbin.