let the air evacuate and to obtain a final product with better mechanical characteristics. After all the fabric layers have been put in the right position, another layer of peel-ply is applied on top, with the same purpose as the first one. A sequence of other layers is added above it: the release film, which separates the laminate from the other layers but still allows the excess resin to pass through; the bleeder, whose main function is to absorb the excess resin; a barrier, to separate the bleeder from the breather; the breather, to distribute the vacuum homogeneously across the external surfaces and to avoid any folds of the vacuum bag being transferred to the laminate surface; the vacuum bag, a flexible polymeric film, typically made of nylon, able to maintain the vacuum created with a vacuum pump. Further important elements are the valves and the sealant used to hermetically seal the vacuum bag.This process can be manual, semi-automatic or completely automatic. When done entirely by hand, lamination is a long and difficult process (due to the strict tolerances required). An alternative is a semi-automatic - also called "mechanically assisted" - process, consisting of a machine which handles the layers, which are then applied on the mould by an operator. It is completely automatic if a machine, such as an automatic tape laying machine, can also place the layers in the right position and orientation. These automatic methods allow high production rates to be reached. Polymerization Polymerization of the laminate is the third and final stage of the Lay-Up process. This phase is of utmost importance to obtain the required characteristics of the final product. Polymerization in autoclave and industrial oven This process can be done at room temperature with just a vacuum pump, to control vacuum, with the aid of an industrial oven connected to a vacuum pump, to control temperature and vacuum, or with an autoclave, to control temperature, vacuum and also hydrostatic pressure. Polymerization in an autoclave is a technique which allows laminates with the best mechanical properties to be obtained, but it is the most expensive and permits only the use of open moulds. The advantage is due to the fact that the pressure helps to bond the composite layers and to eject air inclusions and volatile products, increasing the quality of the process. Each combination of fabric and resin has its own optimal polymerization cycles,