A method of manufacturing an aerofoil for a gas turbine engine (10). The method comprises the steps of providing first and second panels (16, 18), providing a web (30) between the first and second panels, deforming the panels and the web by applying internal pressure between the panels so as to form a series of internal cavities partitioned by the web. The method further includes the step of either cutting the web (30) across its entire width or causing the web to fail across its entire width so as to define an aerofoil having first and second panels with at least one protrusion extending from the first panel partially across the space between the first and second panels.