A method of producing ultra-low density fiber composite (ULDC) foam materials using natural fibers with gas injection through liquid foaming is disclosed, wherein in a particular embodiment includes also cellulose filaments. The method includes a continuous overflow foaming process and a novel apparatus to produce the ULDC materials. The disclosed ULDC composite foam produced includes moisture, mold, decay and fire resistant properties which can be used for building thermal and acoustic insulations, protection packaging, air filter products, hygiene products. The apparatus comprise a vessel, counter rotating dual impellor, a plurality of baffles and gas injection that produce.