Method of manufacturing wind turbine blades having composite materials is provided that includes selecting an outer mould part, selecting an inner mould part, wherein at least a part of the surface of the inner mould part comprises a compressible layer being covered by an airtight membrane, positioning the composite materials in a mould cavity between the outer mould part and the inner mould part, evacuating the mould cavity, and bonding the composite materials, evacuating the compressible layer before positioning the composite materials.