The mineral fiber forming apparatus (10) having electrodes (14) for heating heat softenable mineral material to form a molten mineral mass is disclosed. Organically-coated glass fiber scrap and cullet are supplied to a vessel (12) providing the heat softenable mineral material. An impeller (16) turbulently mixes the molten mineral mass dispersing batch into the molten mineral mass and converting water in the molten mineral bath to steam. Molten mineral material formed by the appartus (10) includes small seeds and gaseous occlusions. The molten mineral material is fed from an outlet port (24) in the vessel (12) to a rotary spinner (30) which forms hollow mineral fibers (32) having gaseous occlusions of between 1 % and 10 % by volume by centrifuging the molten mineral material.