Breather cloth and mesh

Breathable materials and exhaust materials play two roles respectively, but usually at the same time. The role of exhaust materials is to absorb excess resin that "flows out" from the ply, which is usually discharged through a perforated release film (sometimes just a peel layer). The role of "breathable materials" is to create a vacuum over the entire surface, allowing air to be completely expelled from between the bag and the parts Perfusion typically uses a surface flow medium that allows the resin to flow easily across the top of the laminate, rather than laboriously through all the fibres. The resin simply fills the laminate layer "down" from the surface. This speeds up perfusion and allows for greater spacing of the feed lines.