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An intermediate stage in the reaction of a thermosetting resin in which the material melts when heated and dissolves in certain solvents. Materials are usually precured to this stage to facilitate handling and processing prior to final cure.

Bag Moulding

A process in which the consolidation of the material in the mold is effected by the application of fluid or gas pressure through a flexible membrane.

Bag Side

The side of the part that is cured against the vacuum bag.


Applying an impermeable layer of film over an uncured part and sealing the edges so that a vacuum can be drawn.

Balanced Construction

Equal parts of warp and fill in fiber fabric. Construction in which reactions to tension and compression loads result in extension or compression deformations only and in which flexural loads produce pure bending of equal magnitude in axial and lateral directions.

Balanced Laminate

A composite laminate in which all laminate at angles other than 0o and 90o occur only in + pairs (not necessarily adjacent) and are symmetrical around the centerline.

Bare Glass

The glass as it flows from the bushing in fiber form, before a binder or sizing is applied.

Bi-Directional Laminate

A reinforced laminate in which the fibres are oriented in 2 directions.

Bias Fabric

A fabric in which warp and fill fibres are at an angle to the length.

Biaxial Winding

A type of filament winding in which the helical band is laid in sequence, side by side, with no crossover of the fibres.


A coating applied to the surface of a chopped glass mat or preform which is then cured. The binder holds the previously sized glass bundles or ends together in the roving operation into a stable shape or form.


A large collection of continuous glass bundles which is tangled up and will not run through the guide eye into roving creel. In the field, a large tangled collection of roving which does not run through the tube or guide eyes to the chopper.

Bisphenol A

A condensation product formed by reaction of two (bis) molecules of phenol with acetone (A). This polyhydric phenol is a standard resin intermediate along with epichlorohydrin in the production of epoxy resins.


An elastomeric lining for the containment of pressurisation medium in filament-wound structures, or for the manufacture of composite structures.

Blade Packing

Glass bundles or chopper fuzz which build up and pack between the blades of a chopper. This blade packing can cause poor choppability. If it falls off, it usually does not wet-through, and this can cause blisters or porosity.

Bleeder Cloth

A nonstructural layer of material used in the manufacture of composite parts to allow the escape of excess gas and resin during cure. The bleeder cloth is removed after the curing process is complete and is not part of the final composite.


The excess liquid resin appearing at the surface primarily occurring during filament winding.


Undesirable rounded elevation of the surface of a plastic, whose boundaries may be more or less sharply defined, resembling in shape a blister on the human skin. The blister may burst and become flattened.


Bulk Moulding Compound. Thermosetting resin mixed with strand reinforcement, fillers, and so on, into a viscous compound for compression or injection moulding. See also sheet moulding compound.


The spool or shipping package on to which textile yarns are wound.

Boron Fibre

A fibre usually of a tungsten-filament core with elemental boron vapor deposited on it to impart strength and stiffness.


A narrow tubular or flat fabric produced by intertwining a single set of yarns according to a definite pattern.


See Dispersion.


A loosely woven material, such as glass fabric, which serves as a continuous vacuum path over a part but does not come in contact with the resin. The breather is removed after the curing process is complete and is not part of the final composite.


Condition in which fibres do not move into or conform to radii and corners during moulding, resulting in voids and dimensional control problems.

Broad Goods

Fibre woven to form fabric up to 1270 mm (50 in.) wide. It may or may not be impregnated with resin and is usually furnished in rolls of 25 to 140 kg. (50 to 300 lb).

Broken End

In the roving operation, a broken or severed strand (bundle) which causes the forming cake to stop running.


Glass bundles or chopper fuzz which collect on the chopper, cot, static bars or machine frame.

Bulk Factor

The ratio of the volume of a raw moulding compound, reinforcement or powdered plastic to the volume of the finished solid piece produced therefrom. The ratio of the density of the solid plastic object to the apparent or bulk density of the loose moulding powder or fabric.

Bulk Moulding Compound (BMC)

Thermosetting resin mixed with strand reinforcement, fillers, and so on, into a viscous compound for compression or injection molding. See also sheet moulding compound.


A discrete collection of many parallel glass filaments. A collection of Individual filaments, a sub-strand.


Plate with holes through which molten glass is pulled to produce glass fibres.

Bushing Tip

Small tapered protrusions on the bottom of bushings each containing an orifice through which molten glass flows, from which continuous filaments are drawn.