• Composite materials: a material formed from adding together two existing materials to exploit their benefits. Normally, constituents can be physically/visually identified.
• Fibers: Reinforcement materials provide composites with mechanical performance: excellent stiffness and strength, as well as good thermal, electrical and chemical properties, while offering significant weight savings over metals.
• Matrix: The role of the matrix is to support the fibres and bond them together in the composite material. It transfers any applied loads to the fibres, keeps the fibres in their position and chosen orientation. The matrix also determines environmental resistance and maximum service temperature of a prepreg. When selecting prepreg the maximum service temperature is one of the key criteria for choosing the appropriate prepreg matrix.
• Orthotropy is the condition expressed by variation of mechanical properties as a function of orientation.
• Residual stresses: One consequence of the microscopic heterogeneity of a composite material is the thermal expansion mismatch between the fiber and the matrix. This mismatch causes residual strains in the lamina after curing. The corresponding residual stresses are often assumed not to affect the material’s stiffness or its ability to strain uniformly.
• The interlaminar shear strength (ILSS) of fiber reinforced composites describes the shear strength between laminate planes of composites and is determined using the short beam shear test.
• Shrinkage:  is due to the resin molecules rearranging and re-ordering themselves in the liquid and semi-gelled phase.
• Glass transition temperature (Tg): Tg is the temperature which marks a physical phase change in the matrix properties and gives an indication of its maximum service temperature.
• Composite density: Mass per unit volume g/cm3.
• Degree of cure: Assessment of prepreg advancement and cure characteristics.
• Gel time: The time, at a given temperature, when the matrix progresses from liquid to solid. Indicated by a rapid increase in matrix viscosity.
• Viscosity: Measurement of the flow characteristics of matrices, which are influenced by temperature and heat up rates. More viscosity means less “liquid” or that flows less.
• Tack: A measurement of the capability of an uncured prepreg to adhere to itself and to mould surfaces
• Flow: Percentage weight loss of matrix from a weighed test specimen under agreed conditions of temperature and pressure.
• Dwell: used to equalise tool and component temperatures and to initiate a controlled prepreg cure.
• Viscoelastic properties: The simplest description of time-dependence is linear viscoelasticity. Viscoelastic behavior of polymers manifests itself primarily in shear and is negligible for isotropic stress and strain.
• Deformations are also produced by temperature changes and by absorption of moisture in two similar phenomena.
• Expansion coefficient: Fibers have significantly smaller thermal expansion coefficients than do polymeric matrices. The expansion coefficient of glass fibers is 2.8 x 10-6 in/in/F° (5.0 x 10-6 m/m/C°) while a typical epoxy value is 30 x 10-6 in/in/F° (54 x 10-6 m/m/C°). Carbon and graphite fibers are anisotropic in thermal expansion. The expansion coefficients in the fiber direction are extremely small, either positive or negative of the order of 0.5 x 10-6 in/in/F° (0.9 x 10-6 m/m/C°). When a laminate absorbs moisture, there occurs the same phenomenon as in the case of heating. Again, the swelling coefficient of the fibers is much smaller than that of the matrix. Free swelling of the layers cannot take place and consequently internal stresses develop.
• Anisotropic: Not isotropic; having mechanical and/or physical properties which vary with direction relative to natural reference axes inherent in the material.
• Binder: A bonding resin used to hold strands together in a mat or preform during manufacture of a molded.
• Cure Stress: A residual internal stress produced during the curing cycle of composite structures. Normally, these stresses originate when different components of a lay-up have different thermal coefficients of expans.
• Delamination: The separation of the layers of material in a laminate. This may be local or may cover a large area of the laminate. It may occur at any time in the cure or subsequent life of the laminate and may arise from a wide variety of causes.

Consumables for vacuum bag processing:

• Release agent: Allows release of the cured prepreg component from the tool.
• Peel ply (optional): Allows free passage of volatiles and excess matrix during the cure. Can be removed easily after cure to provide a bondable or paintable surface.
• Bleeder fabric (optional): Usually made of felt or glass fabric and absorbs the excess matrix. The matrix flow can be regulated by the quantity of bleeder, to produce composites of known fibre volume (see calculation)
• Release film: This layer prevents further flow of matrix and can be slightly porous (with pin pricks) to allow the passage of only air and volatiles into the breather layer above.
• Breather fabric: Provides the means to apply the vacuum and assists removal of air and volatiles from the whole assembly. Thicker breathers are needed when high autoclave pressures are used.
• Edge dam: Contains resin flow and component shape.
• Vacuum bag/sealant tape: Provides a sealed bag to allow removal of air to form the vacuum bag