Dietary fiber comprising cellulose, a linear β-(1→4)-linked D-glucopyranose polymer, and hemicelluloses, branched heteropolysaccharides of xylose, mannose, glucose and other sugars. These insoluble polysaccharides form plant cell walls, resist human digestive enzymes, and promote gastrointestinal motility, fecal bulk, and short-chain fatty acid production via colonic fermentation. Cellulose provides structural rigidity while hemicelluloses contribute matrix flexibility. Both are non-digestible, calorie-free, and exhibit high water-holding capacity without dissolving. They lower glycemic response and cholesterol absorption indirectly through physical effects. Thermal decomposition occurs above 250 °C without melting or boiling. Widely studied in nutrition science for benefits in preventing constipation, diverticulosis, and metabolic disorders.