Hemp Bast Fiber

Hemp bast fiber is the long, strong, fibrous material found in the outer layer of the hemp stalk — between the bark and the woody inner core. The bast fibers are the plant’s vascular phloem tissue, evolved to transport sugars from leaves to roots; their structural role gives them the tensile properties that have made hemp one of the most consequential fiber crops in human history.

For at least 8,000 years, human beings have grown hemp principally for these fibers. The earliest archaeological hemp textiles — fragments from sites in China and Central Asia — date to approximately 6000 BCE. Hemp rope and sailcloth substantially enabled the European Age of Sail (the word canvas derives from the Latin [[cannabis|cannabis]]); the U.S. Constitution drafts were written on hemp paper; ship rigging on every major navy in the world from antiquity through the 19th century was substantially hemp.

Material properties

A non-exhaustive list of what makes hemp bast distinctive:

• Length. Individual hemp bast fibers reach 1–5 meters, limited by the height of the stalk. Most plant fibers (cotton, ramie, sisal) are substantially shorter. The long-fiber length is what allows hemp to be spun into strong yarn with relatively few twists.
• Tensile strength. Hemp bast has a tensile strength of roughly 550–900 MPa, comparable to or exceeding flax and substantially stronger than cotton. The strength derives from the high cellulose content (roughly 70–80%) and the helical winding angle of the cellulose microfibrils.
• Durability. Hemp fiber resists UV degradation, microbial attack, and saltwater far better than cotton or wool. Hemp ropes were preferred for naval applications in part because they did not rot in seawater [[daoism|the way]] other fibers did.
• Hygroscopic and breathable. Hemp absorbs moisture readily and releases it readily; hemp textile is comfortable in both hot and cool conditions.
• Lustre. Properly processed hemp has a substantial natural shine, comparable to linen.
• Roughness, in raw form. Untreated hemp is coarse and stiff. The contemporary apparel industry uses enzymatic, alkaline, or mechanical softening processes to produce the soft hemp textiles now common in clothing — these processes were not historically available, which is why historic hemp clothing has a reputation for being rough.

Processing

Hemp bast must be separated from the woody hurd and from the pectins that bind the fibers together. The traditional process:

1. Cutting. Stalks are cut at the base when the plant is at the proper stage (typically before full seed maturity for highest fiber quality).
2. Retting. A controlled microbial-decomposition process that breaks down the pectin matrix holding the bast fibers to the hurd. Methods include [[retting|dew retting]] (stalks left in the field for several weeks; cheapest, lowest quality control), water retting (stalks submerged in ponds or rivers; higher quality, environmentally complicated), and enzyme retting (modern controlled process using purified enzymes; highest quality, highest cost). See [[retting]] for detail.
3. Drying. Retted stalks are dried to consistent moisture content.
4. Breaking and scutching. Mechanical processing breaks the woody hurd into small pieces and beats it away from the bast fibers. See [[hemp-decortication]].
5. Hackling. Combing the long fibers parallel and removing short fibers (tow) and remaining hurd dust.
6. Spinning. The cleaned long fibers are spun into yarn; the tow can be spun into coarser yarn or used in non-woven applications.

The processing is substantially more involved than cotton processing, and the contemporary U.S. textile-processing infrastructure for hemp is thin — most hemp apparel sold in the U.S. is processed in China, where the infrastructure has been continuous.

Applications

A non-exhaustive map:

• Apparel textiles. Hemp clothing, often blended with cotton or organic fibers; has grown substantially in the contemporary natural-fiber market.
• Industrial textiles. Geotextiles for erosion control, agricultural mulch fabric, filter media, sailcloth, canvas, work clothing.
• Rope and cordage. Historically the principal application; continues in marine and specialty contexts.
• Automotive composites. Hemp-fiber-reinforced composites are used in interior panels, dashboards, and trunk linings by BMW, Audi, Mercedes, and others. Lighter than fiberglass, more sustainable, comparable strength.
• Specialty paper. Hemp paper is exceptionally durable (early hemp papers from the 13th century survive in better condition than contemporaneous wood-pulp papers). Continuing applications in archival paper, currency (some national currencies have included hemp fiber), and fine paper.
• Insulation. Hemp-fiber batts are now produced as building insulation; see [[hemp-fiber-insulation]].

See also

Auto-generated from this entry’s typed relations: frontmatter, grouped by relation type so the editorial signal isn’t flattened.

• Subset of: [[hemp]]
• Member of: [[ingredient]]
• Used by: [[americhanvre]]
• Supersets: [[hemp-fiber-insulation]] · [[hempwood]]
• Enabled by: [[retting]]

Sources

1. Robert C. Clarke & Mark D. Merlin. [[cannabis|Cannabis]]: Evolution and Ethnobotany. University of [[berkeley|California]] Press, 2013. Source class: book / definitive scholarly survey.
2. John Roulac. Hemp Horizons: The Comeback of the World’s Most Promising Plant. Chelsea Green, 1997. Source class: book / accessible historical and contemporary survey.
3. Jack Herer. The Emperor Wears No Clothes. AH HA Publishing, 1985 (rev. multiple editions). Source class: book / advocacy-oriented historical compendium; useful for source-leads.
4. International Hemp Association — technical publications. Source class: institutional / continuing technical body.

Lenses still to grow

• Hemp paper and the historical-archaeological evidence for early Chinese hemp paper.
• The contemporary hemp apparel supply chain and its concentration in China.
• Automotive bio-composites as continuing application.
• The retting question in detail — environmental tradeoffs across methods.