Vacuum Bag Moulding

A process in which a sheet of flexible transparent material plus bleeder cloth and release film are placed over the lay-up on the mould and sealed at the edges. A vacuum is applied between the sheet and the lay-up. The entrapped air is mechanically worked out of the lay-up and removed by the vacuum, and the part is cured with temperature, pressure, and time. Also called bag moulding.

Vacuum-Assisted Resin Transfer Moulding (VARTM)

An infusion process where a vacuum draws resin into a one-sided mould. A cover, either rigid or flexible, is placed over the top to form a vacuum-tight seal.


An ultra thin mat similar to a surface mat, often composed of organic fibres as well as glass fibres.


A small hole or shallow channel in a mould that allows air or gas to exit as the moulding material enters.


A physical and mechanical discontinuity occurring within a material or part which may be two-dimensional (e.g., disbonds, delaminations) or three-dimensional (e.g., vacuum-, air-, or gas-filled pockets). Porosity is an aggregation of micro-voids. Voids are essentially incapable of transmitting structural stresses or nonradiative energy fields. 

Void Content

Volume percentage of voids, usually less than 1% in a properly cured composite. The experimental determination is indirect, that is, calculated from the measured density of a cured laminate and the "theoretical" density of the starting material.


Materials, such as water and alcohol, in a sizing or a resin formulation, that are capable of being driven off as a vapour at room temperature or at a slightly elevated temperature.