Seminar notes · Botany & materials
Hemp science: unravelling the world’s most popular plant
Hemp turns up in three very different seminar rooms: the materials lab, the pharmacology lecture and the architecture studio. These notes bring the three together. They cover how the plant’s fibres soak up sound, how its compounds interact with the body’s endocannabinoid receptors, and why builders are casting walls from its woody core and lime.
One plant, three industries
Hemp is Cannabis sativa grown for fibre, seed and other compounds rather than for intoxication. In the United States, the 2018 Farm Bill defines industrial hemp as cannabis containing no more than 0.3 percent delta-9 tetrahydrocannabinol (THC) by dry weight. Above that line, the same species is regulated as marijuana.
The stalk is where the materials science lives. It has two main parts. The outer layer holds the bast fibres: long, strong strands made mostly of cellulose that once supplied the world’s rope and sailcloth. The woody inner core, called hurd or shiv, breaks into light, porous chips. A mechanical process called decortication separates the two. The seeds go to food and oil, and the flowers to the extraction of compounds such as cannabidiol (CBD).
Bast fibre and acoustic insulation
Hemp fibre insulation comes as soft batts or boards, usually bound with a small share of polyester fibre so it keeps its loft. Its thermal conductivity is typically around 0.040 W/m·K, in the same range as mineral wool. It is pleasant to handle, needs no itchy-fibre precautions, and can absorb and release moisture without losing much performance.
Acoustically, it behaves as a porous absorber. Sound waves enter the tangle of fibres and lose energy to friction as air moves back and forth through the tiny gaps, turning sound into a very small amount of heat. Porous absorbers work best at middle and high frequencies, such as voices and television dialogue. Low frequencies, like bass from a neighbor’s speaker, need much thicker layers, because absorbers work best when their depth approaches a quarter of the sound’s wavelength.
For a study room in a Baltimore rowhouse, these notes translate into practical advice. Fibre insulation in a shared party wall or a partition between rooms cuts voice-range noise well. But airborne sound travels through gaps far more easily than through walls, so sealing around doors, outlets and pipes often helps more than anything else. Bass needs mass and decoupling, such as an extra layer of drywall on resilient mounts. Our guide to study-room lighting and wiring covers the other half of making a quiet room work.
Hempcrete building envelopes
Hempcrete, also called hemp-lime, is made by mixing hemp hurd with a lime-based binder and water. It is cast around a timber frame, sprayed, or formed into blocks. It is not structural: the frame carries the loads, and the hempcrete provides insulation, thermal mass and a solid, breathable wall.
The numbers explain its appeal. Hempcrete is light, often around 300–400 kg/m³, with a thermal conductivity in the range of roughly 0.06–0.09 W/m·K. Walls are typically a foot thick to reach good insulation values. It is vapor-open, buffering indoor humidity by absorbing and releasing moisture, which helps keep a room comfortable. The lime binder slowly reabsorbs carbon dioxide as it cures, and the hemp itself stored carbon as it grew, so many analyses count hempcrete walls as storing more carbon than they cost to make.
It is also a non-toxic material in use. There are no volatile organic binders, it resists mold and pests well, and lime renders give good fire performance. The cautions are practical: lime is caustic while wet, so gloves and eye protection are essential on site, and walls take weeks to dry before finishing. In the United States, hemp-lime construction now has its own appendix in the 2024 International Residential Code, giving builders and inspectors a shared reference for the first time.
CB1, CB2 and the endocannabinoid system
The pharmacology seminar starts with a system the body already has. The endocannabinoid system is a signaling network that helps regulate appetite, pain, mood, memory and immune responses. Its two best-known receptors are both G-protein-coupled receptors that mostly act through inhibitory G-proteins.
- CB1 receptors are among the most abundant receptors in the brain. They sit mostly on presynaptic nerve terminals, where activating them reduces the release of neurotransmitters.
- CB2 receptors are found mainly on immune cells, including the brain’s microglia, and are associated with inflammation and immune signaling.
The body makes its own ligands for these receptors, chiefly anandamide and 2-arachidonoylglycerol (2-AG). They work in an unusual direction. A receiving neuron makes them on demand and releases them backwards across the synapse to the sending neuron, where they act on CB1 to quiet it down. This retrograde signaling acts as a brake on overactive circuits. Enzymes break the signals down quickly: FAAH for anandamide and MAGL for 2-AG.
Plant compounds join this system in different ways. THC is a partial agonist at both CB1 and CB2, and its action at CB1 explains its psychoactive effects. CBD binds only weakly to the main receptor sites. Research suggests it may act as a negative allosteric modulator at CB1, changing how the receptor responds to other molecules, and that it also acts on other targets such as serotonin 5-HT1A receptors and TRPV1 channels. A purified CBD medicine is approved in the United States for certain severe seizure disorders.
These are seminar notes, not medical advice. CBD can interact with other medicines through liver enzymes such as CYP3A4 and CYP2C19. Anyone thinking about cannabis or CBD products should speak with a doctor or pharmacist first, especially during illness or treatment.
The Maryland context
Maryland legalized adult-use cannabis for people 21 and over on July 1, 2023, with sales regulated by the Maryland Cannabis Administration. Hemp-derived products follow a separate set of rules. For students and visiting families, the practical points are simple: public consumption is not permitted, most hotels and short-term rentals prohibit smoking of any kind, and university campuses in Baltimore set their own strict rules regardless of state law.
Takeaways
- Hemp’s outer bast fibres make effective, pleasant thermal and mid-frequency acoustic insulation, but sealing gaps matters more for a quiet room.
- Hempcrete is a non-structural, breathable, carbon-storing wall material that now has a home in the residential building code.
- The endocannabinoid system uses CB1 and CB2 receptors and retrograde signaling. THC and CBD interact with it in very different ways.
- Hemp’s legal identity rests on a 0.3 percent THC line, and state rules sit on top of that.
For more seminar notes, a study planner and practical guides to Baltimore’s university district, head back to the RMH Baltimore resource guide.