Technical Abstract: Natural fibers traditionally used for cordage are proving valuable for advanced industrial applications due in part to beneficial physical and chemical properties, but also because they are a renewable and biodegradable resource. Kenaf (Hibiscus cannabinus L., Malvaceae) produces high yields of lignocellulosic bast fibers in the bark layer, and is a promising crop for supplying emerging fiber markets. Bast fibers are bundles of cells that undergo extensive cell-wall thickening during maturation. Bundle maturity is an important determinant of fiber quality. Fiber bundles in stem sections of progressive age were analyzed by epifluorescence microscopy, and viscoelastic proprieties were determined by dynamic mechanical analysis. Early-forming primary fibers were larger than later-forming secondary fibers, but cell-wall thickening contributed most to tensile strength and vibration absorption.