A method of manufacturing a blade (20) for a turbomachine by superplastic forming and diffusion bonding a first layer (18), a second layer (16) and a membrane (2), the membrane (2) being disposed between the first and second layers (18, 16), the method comprising: applying a stop-off material in a first predetermined pattern between the first layer (18) and the membrane (2) so as to prevent a diffusion bond from forming between the first layer and the membrane across said first predetermined pattern; and applying the stop-off material in a second predetermined pattern between the second layer (16) and the membrane (2) so as to prevent a diffusion bond from forming between the second layer and the membrane across said second predetermined pattern.