The present invention relates to a container having a cavity, wherein the cavity has a cavity pressure and comprises fibre material suitable for manufacturing one or more fibre-reinforced composite components for a wind turbine blade, and at least a part of the fibre material touches a first part of a wall of the container, at least the first part of the wall consisting of a flexible airtight material, and a ratio of an entire volume of non-cured polymer in the cavity to an entire volume of the fibre material in the cavity is less than 0.3, and the container is adapted to prevent inflow of a polymer into the cavity. A method for preparing such a container is also disclosed. A method for laying fibre material into a mould is also disclosed.