Processes and systems for producing glass fibers having regions devoid of glass using submerged combustion melters, including feeding a vitrifiable feed material into a feed inlet of a melting zone of a melter vessel, and heating the vitrifiable material with at least one burner directing combustion products of an oxidant and a first fuel into the melting zone under a level of the molten material in the zone. One or more of the burners is configured to impart heat and turbulence to the molten material, producing a turbulent molten material comprising a plurality of bubbles suspended in the molten material, the bubbles comprising at least some of the combustion products, and optionally other gas species introduced by the burners. The molten material and bubbles are drawn through a bushing fluidly connected to a forehearth to produce a glass fiber comprising a plurality of interior regions substantially devoid of glass.

Provided are flat-cross-section glass fiber that is superior in continuous-production efficiency and mass-production suitability and able to give superior reinforcing ability for resin molded products, and a method for manufacturing flat-cross-section glass fiber from a glass raw material containing a recycled glass material. In the flat-cross-section glass fiber of the present invention, flat-cross-section glass filaments constituting the flat-cross-section glass fiber each have a flat cross-sectional shape having a major axis with a length in a specific range and a minor axis with a length in a specific range, and the coefficient of variation for the lengths of the minor axes is within the range of 8.0 to 26.1%.

Provided are flat-cross-section glass fiber that is superior in continuous-production efficiency and mass-production suitability and able to give superior reinforcing ability for resin molded products, and a method for manufacturing flat-cross-section glass fiber from a glass raw material containing a recycled glass material. In the flat-cross-section glass fiber of the present invention, flat-cross-section glass filaments constituting the flat-cross-section glass fiber each have a flat cross-sectional shape having a major axis with a length in a specific range and a minor axis with a length in a specific range, and the coefficient of variation for the lengths of the minor axes is within the range of 8.0 to 26.1%.