Last updated on July 22, 2026 · Originally published June 11, 2018
One of the most important properties of an extraction solvent is its polarity — a measure of how electrical charge is distributed across its molecules. Polarity strongly influences which compounds a solvent can dissolve, and it explains much of what separates butane, ethanol, CO2, and the other solvents on the shelf — although temperature, pressure, water content, contact time, and the state of the biomass also shape the final result. The useful starting rule: cannabinoids and terpenes are largely non-polar, so non-polar solvents capture them selectively, while polar solvents recover those compounds along with more of the surrounding plant material.
What Does “Polarity” Actually Mean?
Polarity comes down to how atoms in a molecule share their electrons. When they share equally, the molecule is non-polar and electrically balanced; when they share unequally, one region carries a slight negative charge and another a slight positive one, making the molecule polar. Water is the classic polar molecule; oils are non-polar. The two don’t mix well because each interacts more favorably with molecules of its own kind — and that same principle is a central basis of solvent selection.
The compounds most extractors want — the cannabinoids and terpenes concentrated in the plant’s trichomes — behave largely like oils and are mostly non-polar. Many unwanted constituents, including water-soluble sugars, are more polar. But the division isn’t clean: chlorophyll contains both a polar region and a large hydrophobic tail (which is exactly why a solvent like ethanol pulls it so readily), while plant waxes are largely non-polar despite often being undesirable. “Like dissolves like” is therefore a useful starting rule, not a complete prediction — temperature, solvent composition, water content, and contact time can all shift selectivity even when the solvent stays the same.
There’s one important nuance worth knowing, because it complicates the tidy “cannabinoids are non-polar” rule. In the living plant, cannabinoids exist mostly in their acidic forms — THCA and CBDA rather than THC and CBD. The acidic cannabinoids are somewhat more polar than their neutral counterparts because they retain a carboxylic acid group, which can improve their recovery in alcohols or in CO2 systems using a polar co-solvent. But they remain predominantly lipophilic molecules rather than genuinely water-soluble ones. Whether the starting material has been decarboxylated therefore shifts the calculation, which is one more reason solvent selection isn’t as simple as sorting compounds into two bins.
Non-Polar Solvents: Butane, Hexane, and Propane
Non-polar solvents are the go-to for clean, selective cannabinoid and terpene capture. Butane and propane — the hydrocarbons behind BHO — dissolve the non-polar resins from the trichome heads while leaving behind much of the polar, water-soluble material, which is part of why a well-made hydrocarbon extract can be light-colored and flavorful rather than dark and vegetal. Butane in particular is prized for capturing terpenes. (Extraction facilities use high-purity hydrocarbons manufactured for processing applications, rather than consumer lighter-refill products.)
Hexane
Hexane is another non-polar hydrocarbon, used extensively in industrial oil extraction. Its higher boiling point makes it less convenient to remove than butane or propane, and concerns around worker exposure and residual-solvent limits make it less attractive for many cannabis applications. The common thread across this group is selectivity: because they’re non-polar, they recover fewer of the water-soluble and amphiphilic plant constituents that can make broader-spectrum crude extracts darker and more vegetal.
Polar Solvents: Ethanol and Isopropanol
Ethanol is the workhorse of commercial cannabis extraction, largely because of its safety profile and versatility — but its polarity is a genuine double-edged sword. Because ethanol can interact with a broad range of compounds, it may also recover chlorophyll, waxes, pigments, and other components of the plant matrix, producing a darker crude that typically needs additional refinement such as winterization. Extractors limit that co-extraction by lowering the temperature and shortening contact time: cold conditions reduce the solubility or slow the extraction of many unwanted compounds, though the effect varies by compound and process. This is the principle behind quick-wash ethanol (QWET) extraction, a technique built specifically around limiting ethanol’s tendency to over-extract.
Isopropanol is another alcohol sometimes used, typically as a wash or secondary solvent rather than a primary one. Like ethanol, it dissolves cannabinoids but also extracts a broad range of plant constituents. Because it’s a Class 3 residual solvent, manufacturers have to remove it adequately and verify the finished extract against applicable residual-solvent limits.
The Special Case of CO2
Supercritical CO2 is a low-polarity solvent, but unlike ordinary liquid solvents, its density and solvent strength can be adjusted by changing pressure and temperature. Those changes alter which compounds dissolve most readily, how selectively they’re extracted, and how quickly they’re recovered — giving operators an unusually broad degree of control over solvent strength. Polar co-solvents such as ethanol can also be added when greater recovery of relatively polar compounds, including the acidic cannabinoids, is desired. That tunability, combined with the fact that CO2 is non-flammable and readily separates from the extract when the system is depressurized, is a large part of its appeal. The tradeoffs are that the equipment is expensive and requires trained operators, and the extract often still needs post-processing.
Why It Comes Back to Polarity — and What Else Matters
Polarity provides the basic framework for solvent selection, but operating conditions determine how that framework plays out in practice. Non-polar hydrocarbons offer clean selectivity at the cost of flammability and tight regulation; polar ethanol offers safety and scale at the cost of co-extracting more of the plant; CO2 offers tunability and a clean finish at the cost of complexity. Within any of those choices, temperature, contact time, water content, and the state of the biomass all move the result too — so there’s no universally “best” solvent, only the one whose tradeoffs fit the product, the scale, and the regulatory setting.
This article is part of T&T’s complete guide to BHO extraction, which covers how these solvents are used in practice.
Originally published 2019. Updated July 2026 to correct the acid-versus-neutral cannabinoid solubility nuance, clarify how supercritical CO2’s solvent strength is tuned, and add current sourcing.
