Hemp Glossary


Bast fiber, or just bast, is the stringy fiber that makes up about 25 percent of the hemp stalk. It is located in the phloem, the layer between the core and the outer skin, and is harvested via a retting process that separates it from the hurd portion of the plant stem.

There are two categories of bast fiber, primary and secondary. The primary bast fibers are the most valuable part of the stalk. They make up 70-90% of the bast. They are 5 to 50 mm long, have a high cellulose density (50-70%), and are low in lignin (4-10%). They have been used for centuries to make paper, rope, canvas, textiles, plastics, and much more.

The secondary bast fibers make up 10-30% of the bast, are high in lignin, and are much shorter than primary bast fibers, only about 2 mm in length, making them much less desirable.


Hemp biomass is all the plant material remaining after the seeds and flowers are harvested. Basically, anything not used for human or animal food, like the stalks and leaves, are considered biomass.


Hemp stalks contain an inner core called hurd, or hurd fiber. It is a short fiber (about 0.5 mm long) that is high in lignin (20-30%) and is used to make animal bedding, fuel, bioplastic, and construction materials, like insulation, acoustical tiles, hempcrete, and much more.

Pyrolytic conversion (pyrolysis)

Pyrolysis is the process of applying high heat to solid organic material, or biomass, in the absence of oxygen. In the case of hemp, pyrolysis can be used to expedite the decomposition of hemp stalks to produce fuels, industrial feedstocks, and other uses.


The process of separating bast fibers from the less desirable parts of the hemp stalk. Retting is a microbial process that breaks the chemical bonds that hold the stem together and allows for separation of the bast fibers from the woody core, or hurd fibers.
There are two traditional types of retting. Field or dew retting, is done by cutting down the plant stems and allowing them to rot in the field until the bast fibers separate from the inner core.
The second method is water retting whereby stems are immersed in water until separation occurs.
For further information see the USDA's Harvesting, Retting, and Fiber Separation (pdf)