Jars, Grove Bags or Humidity Packs: What Actually Works?

Glass jars, multilayer bags and humidity-control packs address different aspects of cannabis storage. Their usefulness depends on how they manage moisture exchange, oxygen, light and physical protection over the intended storage period. Temperature and the condition of the flowers when they enter the container are equally important.

A comparison based on those functions is more useful than choosing between brands alone. No package preserves every compound indefinitely, and a container cannot compensate for material that was insufficiently dried before storage.

What storage needs to protect

Once flowers have been correctly dried, storage should keep water activity reasonably stable, limit conditions that favour microbial growth, prevent excessive moisture loss and reduce handling damage. It should also slow unwanted changes in cannabinoids and volatile aroma compounds.

These goals can overlap without being interchangeable. A package may provide a strong moisture barrier without actively adjusting humidity, while a humidity pack may buffer water-vapour exchange without providing the light or physical protection of the surrounding container.

Glass jars and the importance of the seal

Glass provides an effective barrier to gases and water vapour, is chemically inert and does not readily absorb aroma compounds. The performance of a complete jar still depends on its lid and seal. A well-sealed container limits exchange with the surrounding room and can help keep moisture stable.

That barrier does not regulate moisture by itself. Flowers sealed too wet remain in a humid enclosed environment, while an empty jar has no source of water with which to correct material that is too dry. Starting water activity therefore matters as much as the choice of glass.

Clear jars also transmit light. Keeping them in darkness avoids unnecessary light exposure during storage. Research has found greater cannabinoid-profile changes at room temperature than under cooler conditions, so the environment around the container remains relevant even when its seal is effective.

Multilayer bags are not one material specification

Flexible multilayer packaging can provide useful barriers while being lighter and less fragile than glass. However, the name “Mylar bag” does not specify the permeability of every product sold under that description. Different laminates, closures and seals allow different rates of oxygen and water-vapour exchange.

Whether flowers gradually lose moisture depends on the package, the humidity gradient and the storage conditions. Comparing barrier performance and closure quality is therefore more informative than assuming that all bags behave alike.

What the Grove Bags evidence does and does not establish

Grove Bags use a proprietary multilayer film marketed as TerpLoc. The proposed function is controlled passive exchange of gases and water vapour, intended to help stabilise the enclosed environment without routine opening.

In May 2026, the US National Advertising Division reviewed supporting data and found a reasonable basis for certain condition-dependent claims about moisture stability and preservation of cannabinoids and terpenes compared with conventional storage when product instructions were followed. It also recommended modifying or discontinuing other claims.

In particular, the evidence did not establish that the packaging consistently maintains exactly 58–62% relative humidity under all conditions. NAD recommended clearer disclosure of conditions of use and avoiding guaranteed or universal performance claims. Grove Bags also voluntarily discontinued mould-prevention claims during the proceeding.

This was an advertising-evidence assessment, not a peer-reviewed experiment establishing that the product is superior to every glass jar or alternative package. It supports a more limited, condition-dependent interpretation than a universal ranking of storage methods.

Comparisons in cannabis research

Baek, Grab and Chen (2025) compared three weeks of curing in glass jars and Mylar bags after different drying treatments. The experiment used the cannabinoid-type hemp cultivars Hempress and Wild Bourbon. Total cannabinoid concentrations did not change significantly over the curing period, but the study was not a direct test of Grove Bags or humidity packs.

Spadafora and colleagues (2024) compared other storage arrangements and found differences in volatile profiles and cannabinoid transformations. None of the tested treatments preserved the volatile profile immediately after drying unchanged. Packaging influenced the course of storage, rather than preventing all chemical change.

Oxygen effects depend on the measured compound

Reducing oxygen exposure is relevant to oxidation, but its benefit should be assessed from measured outcomes rather than assumed to be large for every constituent. MacLaughlin and MacDonald (2024) compared sealed cans containing approximately 4% oxygen under nitrogen-modified atmosphere with cans containing normal atmospheric oxygen, approximately 21%. Samples were analysed after 18, 46 and 74 days.

The experiment found no statistically significant difference in total terpenoid concentration attributable to atmosphere treatment or storage time. Individual compounds behaved differently: β-myrcene declined under atmospheric storage but did not show a significant decline under nitrogen-modified atmosphere. The aggregate result therefore does not establish that oxygen had no effect on any aroma compound.

Atmosphere, temperature, moisture, packaging and duration need to be considered together. A result for total terpenoids is not necessarily a result for each individual constituent.

Humidity packs as moisture-management tools

Two-way humidity packs release or absorb water vapour depending on the conditions inside a container. Their purpose is to help maintain a defined equilibrium humidity, rather than produce terpenes or increase potency. ASTM D8197-22 recognises salt-based humidity-control sachets for maintaining dried cannabis within a water-activity range of 0.55–0.65 aw.

At equilibrium and the same temperature, relative humidity divided by 100 corresponds to water activity. A 62% pack therefore does not mean that flowers contain 62% water. Nor does reaching a target water activity remove existing microbial contamination or establish microbiological safety.

A pack may be useful when material is slightly too dry, containers are repeatedly opened, storage is prolonged or a narrow equilibrium-humidity range is important. If correctly dried flowers are already stable in a rarely opened airtight container, little correction may be required. The separate discussion of overdried flowers and controlled rehydration explains the distinction between restoring moisture and recovering lost aroma compounds.

Humidity control should not compensate for flowers sealed excessively wet. ASTM specifies further drying above 0.68 aw rather than relying on a sachet to make wet material suitable for storage.

Interpreting claims about terpene loss

The references discussed here do not establish that correctly designed humidity packs selectively remove valuable terpenes from cannabis. They also do not provide a comprehensive comparison of every material or commercial product.

A change in smell after adding a pack can have several explanations, including changes in how moisture affects volatile release. The strength of the smell when a container is opened is not, by itself, a measurement of retained terpene concentration. Moisture stability is a better-supported reason for using a humidity pack than assuming a predictable change in aroma chemistry.

Temperature, darkness and the condition of the material

Long-term storage research found greater changes in natural cannabinoid composition at 25°C than at lower temperatures. Whole inflorescences stored in darkness under cooler conditions generally retained their cannabinoid profile better, while terpenes declined over time under every tested condition (Milay et al., 2020).

The coldest treatment was not necessarily best for every outcome. Deep freezing and grinding were not favourable for terpene preservation in that experiment, so the findings should not be reduced to a recommendation to freeze all stored flowers.

Before comparing finer packaging differences, establish suitable drying and storage-readiness checks, control water activity, keep material dark and avoid excessive heat. These conditions remain important whichever container is chosen.

Choosing a system for the intended storage period

A well-sealed glass jar offers a reusable barrier but needs protection from light and an appropriate starting moisture condition. A suitable multilayer bag can offer compact, lightweight storage with useful barrier properties. Specialised passive packaging may help manage exchange with the surrounding environment, subject to its conditions of use. Humidity packs provide a separate moisture-buffering function and can be combined with a suitable container.

Evaluate the complete system: its moisture and oxygen permeability, closure, light protection, resistance to physical damage and expected performance over the intended period. None of these options is a universal solution, and none removes the need to begin with appropriately dried material.

References

Baek, Y., Grab, H. & Chen, C. (2025). Postharvest Drying and Curing Affect Cannabinoid Contents and Microbial Levels in Industrial Hemp (Cannabis sativa L.). Plants, 14, 414. https://doi.org/10.3390/plants14030414.

Milay, L. et al. (2020). Metabolic Profiling of Cannabis Secondary Metabolites for Evaluation of Optimal Postharvest Storage Conditions. Frontiers in Plant Science, 11, 583605. https://doi.org/10.3389/fpls.2020.583605.

Spadafora, N.D. et al. (2024). The influence of drying and storage conditions on the volatilome and cannabinoid content of Cannabis sativa L. inflorescences. Analytical and Bioanalytical Chemistry. https://doi.org/10.1007/s00216-024-05321-w.

MacLaughlin, L.L. & MacDonald, M.T. (2024). Is nitrogen-modified atmosphere packaging a tool for retention of volatile terpenes and cannabinoids in stored Cannabis sativa inflorescence? Journal of Cannabis Research, 6, 42. https://doi.org/10.1186/s42238-024-00253-9.

ASTM International (2022). ASTM D8197-22. Standard Specification for Maintaining Acceptable Water Activity Range (0.55 to 0.65) for Dry Cannabis Flower Intended for Human/Animal Use. Standard specification.

BBB National Programs, National Advertising Division (14 May 2026). National Advertising Division Finds Certain TerpLoc® Cannabis Packaging Claims Supported; Recommended Grove Bags Modify or Discontinue Others. Public decision summary. This is an advertising-evidence assessment, not a peer-reviewed research paper.

Featured photograph: My 420 Tours, Cannabis Dispensary flower, CC BY-SA 4.0. Reproduced without alteration. The photograph illustrates glass display containers in a dispensary; the open containers are not a recommendation for prolonged storage.