Short answer
A Boveda pack is a two-way humidity control packet. It releases or absorbs water vapor to hold the air inside a sealed container at a set relative humidity. For cannabis flower, two ratings cover most use: 62% and 58%. Use 62% for curing and for storage of a month or more. Use 58% for flower you will grind and vaporize in the near term.
How a Boveda pack works
Each pack holds a saturated salt solution behind a membrane. Water vapor crosses that membrane in both directions. If the air in the jar is drier than the rating, the pack gives up moisture. If the air is wetter, the pack takes moisture in. The maker states the pack holds a container within about one percentage point of the printed number until the salt solution is spent.
How Should You Store Cannabis for Freshness? A Simple Guide
The pack does not touch the flower. Only water vapor crosses the membrane. Boveda packs are food grade and contain no additives.
Does Freezing Weed Keep It Fresh?
Why humidity matters for weed
Two things happen to dried flower in storage. Terpenes leave. Mold arrives.
Monoterpenes such as myrcene, limonene and pinene are volatile. In dry air they move out of the plant tissue and out of the container. Flower below 55% relative humidity also turns brittle. Trichomes snap off the surface and collect at the bottom of the jar.
Wet flower moves the other way. Above 65% relative humidity, mold and powdery mildew get conditions to grow. ASTM D8197 sets a water activity range of 0.55 to 0.65 for dry cannabis flower. Water activity is not the same measurement as relative humidity, but the two track together inside a sealed jar.
Which rating to pick
- 62%: cure and storage. Best for flower held for weeks or months. Keeps some moisture in the tissue.
- 58%: short term. Common with dry herb vaporizers, since drier flower grinds and vapes with less residue.
- 69%, 72%, 75%: sold for cigars and tobacco. Too wet for cannabis flower.
- 49%, 55%: below the range most growers target for cannabis.
Sizes
Boveda sizes are labeled by weight in grams. Size 1, Size 4, Size 8, Size 67 and Size 320 are sold. Boveda's cannabis chart pairs Size 4 with up to 14 g of flower and Size 8 with up to 28 g. Larger containers and loose lids call for more pack weight.
Rules that matter:
- Do not cut a pack open. The salt solution is not meant to touch plant material.
- Do not add water to a pack.
- One pack per container is enough. Extra packs do not push humidity past the rating.
When to replace
A spent pack turns stiff and grainy. The corners get crisp and the surface feels like cardboard. In a sealed jar opened each day, a Size 8 lasts about 2 to 4 months. A jar that stays closed extends that. Boveda states packs hold their rating longer in airtight containers at room temperature.
Replace the pack when it hardens. There is no way to recharge one.
What a Boveda pack will not do
- It will not bring back terpenes that left the flower.
- It will not kill mold or make moldy flower safe.
- It will not add flavor or weight.
- It will not fix flower kept in a hot, lit room. Keep jars between 60 F and 70 F, in the dark.