Filament

A bundle of parallel, untwisted glass fibre strands wound onto a cylindrical package. Direct rovings feed processes such as filament winding, pultrusion and weaving, while assembled (multi end) rovings are designed for chopping in spray up; rovings are specified by tex and by sizing type.

A bundle of thousands of continuous carbon filaments handled as a single unit, the carbon fibre equivalent of a glass roving. Tows are designated by their filament count in thousands, written with a K, and are used directly in filament winding, automated fibre placement and weaving.

A thin surface treatment applied to fibres during manufacture, typically containing film formers, coupling agents such as silanes, and processing aids. It protects the filaments during handling and, critically, controls adhesion and compatibility between the fibre and the matrix resin, so it must be matched to the resin system in use.

The metric unit of linear density for fibres, strands and yarns, defined as the mass in grams of one kilometre of the product. Glass rovings and yarns are specified by tex, with higher values indicating heavier strands.