A cannabis package has two jobs. The obvious one is compliance and shelf appeal; the quieter one is preservation. Flower is a botanical product, and from the moment it is cured it is under attack from four things: moisture, light, oxygen, and heat. A dispensary can control the temperature, but by the time a jar or bag reaches a customer’s shelf, the packaging is the only defense left standing against the other three. Understanding what each enemy does, and which one your package can actually stop, is the difference between a brand known for fresh, aromatic flower and one quietly known for dry, faded product.

Humidity lives in a narrow band

Cannabis wants a relative humidity most people would find surprisingly specific. The industry-referenced target sits at roughly 55 to 65 percent, and laboratory work narrows the sweet spot further, to somewhere around 59 to 63 percent. That band is narrow because both edges are punishing. Drift above about 65 percent and the extra moisture invites mold and mildew, the kind of contamination that fails a compliance test and endangers a consumer. Drop below about 55 percent and the flower dries out, the trichomes turn brittle and harsh, and the volatile oils that carry aroma and effect evaporate away. The chart below shows why the middle is the only comfortable place to be.

The practical tool is a two-way humidity pack, which both releases and absorbs moisture to hold a target as the surrounding air changes. A 62 percent pack is the common default for flower, while people who vaporize their product often prefer a drier 54 to 58 percent. Including the right pack sizes the package to the product rather than leaving humidity to chance, and it is one of the few preservation choices a brand can build directly into what ships.

Light is the enemy your bag can block

Of the four threats, light is the one packaging defeats most completely. Ultraviolet and even visible light break down cannabinoids, and a frequently cited study from the 1970s concluded that light was the single largest factor in the loss of cannabinoids from stored cannabis. Sunlight is the worst offender, but fluorescent and other indoor lighting contribute too, which matters for product sitting under retail display lights for weeks. The fix is simply opacity. An opaque or heavily tinted package blocks the light before it ever reaches the flower.

This is where clear packaging carries a real cost. A transparent jar or window bag shows off the product, but it also lets in exactly the wavelengths that fade it, so the same feature that sells the flower on the shelf degrades it on the shelf. Brands that want visibility can compromise with amber or smoke tints, small windows rather than clear fronts, or an opaque outer that is only opened at purchase. The point is to treat clarity as a deliberate trade, not a free one.

Oxygen and headspace

The more oxygen the flower sits in, the faster it oxidizes. Air is why barrier matters. A high-barrier film or a genuinely airtight jar slows the exchange of oxygen and moisture between the flower and the outside world, which is the whole reason metallized mylar and foil laminates dominate the category over thin single-layer plastics. The barrier is not just about keeping smell in; it is about keeping air out, and a resealable, well-sealed closure preserves that barrier every time the customer opens and closes the package.

Headspace, the empty air volume inside the package, is the overlooked half of this. A large bag holding a small amount of flower traps a lot of oxygen against the product, and each reseal refreshes that air. Sizing the package close to the fill, or keeping a rigid container around three-quarters full, limits the oxygen the flower has to react with. It is a free improvement that comes purely from matching package volume to product volume rather than defaulting to one oversized format.

Heat and time, the limits of any package

Some degradation no package can prevent. Heat accelerates every other reaction, so the storage target is cool, roughly the mid-fifties to low-sixties Fahrenheit, with sustained temperatures above about 86 degrees to be avoided and brief exposure to real heat, in the region of 110 degrees, doing quick damage. Packaging can insulate a little and can keep light and air out, but it cannot refrigerate, so the honest message to pass to a customer is to store the product somewhere cool and dark once it leaves the store.

Time is the factor nothing defeats. Even under good conditions, potency drifts downward on a fairly predictable curve, with commonly cited figures showing meaningful losses that compound year over year, as the chart below illustrates. Well-designed packaging bends this curve, keeping flower at its best for the first several months to a year, but it does not flatten it. That is exactly why matching production and order sizes to real sell-through matters as much as the film specification does.

Building a package that actually preserves

Preservation is a system, and the pieces reinforce each other. A high-barrier, opaque film handles light and slows oxygen and moisture exchange; an airtight, resealable closure protects that barrier through repeated use; a correctly rated humidity pack holds the flower in its 55-to-65-percent comfort zone; and a package sized close to the fill keeps trapped oxygen to a minimum. Leave any one of those out and the others work harder for less result, because the weakest link sets the pace of decline.

None of this competes with compliance or branding; it sits underneath them. A child-resistant, correctly labeled, beautifully printed bag that still lets in light and air will disappoint the customer who opens it three weeks later. Specify the package to protect the product first, then make it compliant and make it beautiful, and the flower a customer opens will smell and perform the way it did the day it was sealed.

Every flower brand ends up buying mylar bags, and most buyers pick them by eyeballing a size chart and choosing a finish. That works until an eighth rattles around loose in an oversized bag, a batch loses its nose in three weeks, or a compliance officer asks what standard your child-resistant zipper actually meets. The specs on a mylar bag are few, but each one does real work. This is what they mean and how to choose them deliberately.

“Mylar” is a laminate, not a material

The bag on your shelf is a three-layer sandwich. A typical construction is an outer PET (polyester) layer of about 12 microns that carries the print and gives the bag its snap, a middle vacuum-metallized PET layer — PET coated with a few hundred angstroms of aluminum — that does the light and oxygen blocking, and an inner polyethylene layer of roughly 60 to 80 microns that heat-seals shut. “Mylar” is technically a trade name for the PET film, but in cannabis packaging it has come to mean this whole metallized laminate. The practical takeaway: the barrier comes from the metallization and the laminate quality, not from thickness alone, so a well-made 4 mil bag can outperform a cheap thick one.

The size chart, translated to flower

Stock sizes track purchase weights. For 1g samples and promos through 3.5g eighths, the common bag is about 3 by 4 inches; a 3 by 5 inch bag covers eighths with more headroom and 7g quarters; 4 by 6 inches handles quarters through 14g halves; 5 by 8 inches suits halves and 28g ounces; a 6 by 9 inch bag gives an ounce generous room; and pound bags run around 10 by 14 inches for back-of-house and wholesale transfer. The eighth is the volume king for most retail brands, which is why 3 by 5 inch bags are usually the first size worth printing in quantity.

Two sizing habits save money. First, size to the puffiness of your cultivar: fluffy, larded-out flower needs a size up from dense indoor at the same weight, and a bag that needs force to close will eventually fail at the zipper. Second, resist the urge to stock every size in custom print. Most brands do fine printing eighth and ounce bags and using labeled stock bags for the low-volume sizes in between.

Barrier numbers that actually matter

Thickness is quoted in mils — thousandths of an inch — and stock bags typically run 3.5 mil in the small sizes, about 4 mil in the mid sizes, and around 5 mil at a pound. Thicker film means better puncture resistance and a stiffer, more premium hand feel, and premium odor-barrier bags push past 10 mil.

The number fewer buyers check is OTR, the oxygen transmission rate, quoted in cubic centimeters of oxygen passing through 100 square inches of film per day. Typical stock bags spec under 1.0 in small sizes and under 0.5 in mid sizes, while high-barrier pound bags run under 0.1, and top-tier odor-barrier laminates advertise figures far below that. Oxygen is what degrades THC to CBN and flattens terpene profiles, so if shelf life is your problem, ask your converter for the OTR spec before you ask for a thicker bag. Moisture transmission (MVTR) matters too — typical specs run from about 0.5 down to 0.1 grams per square meter per day as bags get more serious — though most brands manage moisture inside the bag with a two-way humidity pack anyway.

Child resistance and opacity are not optional

Adult-use states require child-resistant packaging, and for mylar that means a certified CR zipper tested to the federal protocol in 16 CFR 1700.20 — the standard requiring that the large majority of young children in a test panel cannot open the package. Buy bags with test certification on file, not bags described as “CR-style,” because the paperwork is what an auditor asks for. Many states also require opaque exit packaging, and several restrict imagery that appeals to minors, so a clear-front bag that shows off the flower may be legal in one market and a violation in the next. If you sell across state lines of any kind — multi-state operations, licensing deals — spec the strictest market you serve and use one bag everywhere; it is cheaper than running separate SKUs per state.

Print method sets your minimums

Custom-printed mylar comes off two very different processes. Digital printing has no plates or cylinders, which makes it the right call below roughly 10,000 units per design — short runs, seasonal drops, and brands that revise artwork often. Rotogravure printing engraves a cylinder per color and typically starts at minimums around 10,000 units per design, in exchange for sharper detail, tighter color consistency, and a lower unit price at volume. A common progression is to launch digital, prove the SKU, then move your one or two highest-velocity sizes to gravure once you can commit to five figures of units. Whichever route you take, plan for overseas gravure lead times measured in weeks, not days, and order your next run when the current one is half gone — indicative timing, but running a dispensary drop on unprinted backup bags because the reorder is on the water is the most common self-inflicted wound in this category.

When you request a quote, send five specs: bag size and gusset style, laminate thickness in mils, OTR if shelf life matters to you, certified CR zipper with documentation, and finish plus print method with your expected annual units per SKU. A converter can turn that into an accurate price in one pass — and you will be comparing suppliers on the numbers that determine how your flower actually holds up.