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Paint Cans, Glass Jars, and Mylar, Oh My: The Answer to Training Aid Storage || Precision Explosives
- Yana Allport
- 5 hours ago
- 10 min read
Hi there, science lovers!
A few posts back, we walked through contamination control during imprinting - clean side, dirty side, glove protocols, all that good stuff. Buried near the bottom was a short section on storage, and we get enough questions on that to warrant a post of its own. So which container actually works? Does the material matter? Does this stuff need to live in a fridge? Can it ride around in a patrol vehicle, or does it need its own climate-controlled shelf somewhere? So let's give storage its own time in the spotlight.
Recap on Contamination, Then We Go Further
I'm not going to re-run the whole contamination-control article here - if you haven't read it, it's worth a few minutes. The short version: the Department of Energy's own guidance calls for vapor-tight containers specifically to prevent odor cross-contamination, and a 2024 study on commercial explosives training aids found cross-contamination already present in some products before they'd even left the manufacturing facility.
What that article didn't get into was the part everyone actually wants to know: which container, made of what, actually holds up… and whether the conventional wisdom about cold storage is something you should be following or something you've just absorbed by osmosis because all the cool kids are doing it.
What "Vapor-Tight" Actually Means in Storage
Here's a sentence that sounds reassuring and tells you almost nothing: "I keep it in a sealed container." Sealed against what? Dust? Water? None of those is the same thing as sealed against vapor, and vapor is the only thing that actually matters here.
Forensic chemistry answered this question decades before K9 training got around to asking it, for a different reason. Crime labs processing fire debris for ignitable liquid residue depend on vapor-tight containers so the evidence doesn't leach its own story into the air before it reaches a GC-MS instrument. The guidance from forensic labs is specific: glass mason jars with screw-on lids, or metal cans. Paper and plastic bags are explicitly rejected; they don't qualify as vapor-tight at all.
Nobody at a crime lab is thinking about your detection dog. The physics don't care what's inside the container or who is smelling it. Vapor moves through permeable materials and around bad seals whether it's gasoline residue or diphenylamine or a narcotics. A container that looks closed and a container that's actually vapor-tight are two different categories, and a lot of training aid storage quietly falls into the first one while everyone assumes it's the second.
With that baseline, let's look at the three containers that come up all the time in this community.
Storing Training Aids in Paint Cans
If you've spent any time around explosives detection training, you've seen training aids stored in what looks like a small paint can - and there's a reason that specific form factor stuck around. The Bureau of Alcohol, Tobacco, Firearms and Explosives' National Odor Recognition Test uses a standardized line of paint cans as its testing apparatus, which is part of why some training aid manufacturers size their products to fit those same cans directly.
This isn't an informal habit the community picked up. It's written into the current national standard for training and certifying explosives detection canines. ANSI/ASB Standard 092, published by the AAFS Standards Board for this exact discipline, specifies a clean, unused, perforated container for odor recognition testing and names a metal paint can directly as an example. The same standard separately flags certain highly volatile explosives as needing isolated storage and names a sealed paint can as the example container for that too.
Notice what's not in that spec: a liner. That lines up with how canine researchers have built their own test materials. One fire-service research paper - fittingly titled "Trust Your Dog" - described its canine detection experiments this way: for testing purposes, the researchers used new, clean, unlined quart and gallon cans.
Todd's recommendation matches that exactly: new cans, but skip the liner. An epoxy coating is itself a material with its own odor profile, and that runs against the whole point of using a clean container. A new, bare steel can replaced on a normal training rotation doesn't sit in storage long enough for the lack of a liner to become a corrosion problem. It's not the same job as multi-year courtroom evidence preservation, where some forensic labs do call for lined cans. Different use case, different spec, and the canine-specific standard backs the unlined recommendation.
What this means for you: a brand-new, unlined paint can (no epoxy coating!) or a new glass jar is what Precision Explosives actually recommends. What's still off the table, regardless of lining, is an actual paint can that's had paint in it, even once, even years ago. That's a different problem entirely. You're not avoiding a liner odor at that point, you're storing a training aid against dried paint residue and a seal that's already been worked loose once. New and unused beats reused, no matter what the can is rated for.
There's a second, less obvious reason metal cans hold up well operationally: they don't seem to retain contamination the way porous materials do. Research on residual narcotics odor tested several substrates (cotton washcloths, automotive upholstery, plastic bags, cardboard, HDPE boxes, and metal paint cans) by exposing each to drug odor, then removing the source and testing how long dogs could still detect residual odor on the empty substrate. Cotton, upholstery, and plastic bags held detectable residual odor at a 100% rate even after weeks. Metal paint cans and cardboard dropped to a fifth of that over the same period.
That's a different question than vapor-tightness - it's about what happens after something contaminated touches the container, not about keeping vapor in during normal use. But it's a useful data point if you're rotating containers between odors: a metal can that's been properly cleaned is less likely to be quietly carrying yesterday's odor into today's session than a cotton-lined tote would be. It doesn't replace your clean-side/dirty-side workflow. It just means metal is a forgiving material to build that workflow around.
Glass Jars
Mason jars have been a staple of this community for a long time, and for good reason: they're inert, chemically unreactive, and they don't leach anything into your training aid the way some plastics can. The key word, same as with paint cans, is new. They're also a container type named directly in the same ANSI/ASB "Standard for Training and Certification of Canine Detection of Explosives" above, listed alongside metal containers as a recognized storage option for this discipline.
Glass jars are also what forensic labs default to for vapor-tight evidence storage, which says something about how seriously the seal performance gets taken outside the K9 world too.
Glass has one real limitation: it breaks. A jar that gets knocked off a tailgate or rattles loose in a kit bag is a liability in a way a steel can or a Mylar pouch isn't. Tint doesn't factor into it when it comes to Odor Prints so don't waste time hunting for amber jars specifically. Just handle glass the way you'd handle anything breakable in a kit bag, and you're fine.
Metallized Mylar Bags for Training Aid Storage
This is the one you've probably handled without thinking much about why it works. If you've ever opened an Odor Print, you've held a training aid that ships sealed in metallized Mylar.
Metallized PET — what everyone calls "Mylar," even though true Mylar is the unmetallized base film — posts an oxygen transmission rate as low as 0.01 cc per 100 square inches per day, compared to 150 to 200 cc for plain HDPE plastic. That's roughly a 15,000% improvement in barrier performance. Anything under 1 cc per 100 square inches per day counts as "high barrier" in packaging science. Mylar isn't clearing that bar; it's not even in the same neighborhood as the bar.
That same barrier that keeps oxygen and moisture out is what keeps odor vapor in, and what keeps competing odor out, which matters just as much. It's lightweight, it doesn't rust, it doesn't break, and it folds flat in a kit bag in a way a paint can or mason jar never will. The tradeoff is that the barrier depends entirely on seal integrity. A pinhole or an incompletely sealed corner vents odor the same way a cracked lid does, just less obviously, because nothing looks visibly wrong. Check the seal before you trust it, and don't dig around in the bag with anything that could puncture it.
This is why we package Odor Prints in metallized Mylar to begin with. The barrier isn't there to look professional. It's there because it's the best material for the job.
So Which Storage Method Should You Actually Use?
Match the container to the job. For general storage - a locker, a training room, the back of a vehicle - reach for a new, unlined metal can or a new glass jar. Neither has a liner to introduce odor of its own, and neither cares whether it's tinted. For a kit bag that takes a beating in the field, Mylar wins: it doesn't break, it's light, and a torn pouch is obvious in a way a hairline crack in glass is not.
What doesn't make the list, regardless of material: anything porous, anything that's held a different odor without the wipe-down protocol from the imprinting article, an epoxy-lined can sitting where a bare one should be, and an actual previously used paint can.
Two is Better Than One
Whatever container you're using, PE's recommendation is two layers of packaging between the training aid and the outside world. A TADD inside a Mylar bag, an Odor Print sealed in two Mylar bags, a glass jar inside a sealed outer bag - the specific combination matters less than the principle.
You might be thinking this is overkill, but research measuring explosive vapor transmission through primary containers found that vapor permeates through the inner packaging and accumulates in whatever is around it, even when the primary seal looks intact.
The practical takeaway: a pinhole or an imperfect seal on one layer becomes a non-issue when there's a second layer behind it. It also means that when you open the outer packaging to access a training aid, the inner layer stays uncontaminated until you're ready to work!
The Refrigeration Myth
This is the question we get more than almost any other, and the answer surprises people: it depends on what you're storing, and a lot of handlers are refrigerating things that don't need it because that's just what everyone does.
DHS's own market survey of commercial non-detonable training aids compared storage requirements across the industry, and the spread was wide. Some manufacturers specify refrigeration as the baseline; others set a hard floor of never below freezing, or call for an active freezer on certain odor types while recommending only room temperature or a fridge for the rest of the same product line. There's no single industry standard; storage requirements track to how each product is built.
Our Odor Prints aren't built the same way as products that need to be refrigerated. They're built on POCR (Polymer Odor Capture and Release) media, which captures and releases volatile organic compounds gradually at a stable rate. That's the same property that gives an Odor Print its full year of shelf life. The same DHS report independently noted that Odor Prints require no special storage conditions: refrigeration is not required, and the only real recommendation is a cooler ambient temperature and protection from direct sunlight, nothing close to a fridge, freezer, or climate-controlled room.
That's a direct result of what POCR is doing chemically - releasing odor steadily over time rather than acting like a volatile substance that needs cold storage to slow its own decomposition. Different chemistry, different storage rules.
Can It Live in Your Vehicle?
This is the practical version of the refrigeration question, and the answer is yes. Between sessions, an Odor Print can stay in your vehicle in its original Mylar packaging - no refrigeration, no special case.
The one piece of guidance worth following: keep it out of direct sunlight, same as the cooler-ambient-temperature note above. That's not a warning about instability. It's the same baseline good practice you'd apply to anything you don't want baking on a dashboard all day. A gear bag in the back seat beats leaving it against the windshield for hours. Beyond that, there's no special vehicle-storage protocol to memorize. It's built to handle the kind of day a working K9 team actually has.
CliffsNotes on Detection Dog Training Aid Storage
Storage gets treated like an afterthought because it doesn't feel like training. It is, though - every hour your aids spend in a container is an hour where the odor picture either stays clean or quietly doesn't. Vapor-tight is a measurable property, and not every container that looks sealed has it. Unlined metal, new glass, and metallized Mylar all clear that bar when they're new, intact, and used correctly. An old paint can, an epoxy-lined can, a cracked jar lid, or a punctured Mylar pouch don't, no matter how confident you feel about them.
Depending on what you’re using, your training aids probably don't need to live in a fridge. Check what you're actually storing, and follow what the manufacturer specifies instead of copying whatever everyone else does. Odor Prints are POCR-based and don’t require special storage. We simply recommend storage in a cooler ambient temperature and protection from direct sunlight.
FAQ
Q: What does "vapor-tight" actually mean for a storage container?
It means the container keeps odor vapor in, not just dust or visible contents. A container can look closed and still fail this standard if the material is permeable or the seal is degraded.
Q: Can I reuse an actual paint can that's had paint in it?
No. Residual paint odor competes with the target odor, and a can that's held paint has already had its seal opened and reseated at least once. Use a new, unused can instead.
Q: Should I look for epoxy-lined cans, like the ones forensic evidence labs use?
No. For K9 training aid storage, Precision Explosives recommends the opposite: new cans without an epoxy liner. Forensic labs line their cans because evidence has to survive years without rusting through. A training aid can on a normal rotation doesn't face that timeline, and skipping the liner means skipping a material with an odor profile of its own.
Q: Do Odor Prints need to be refrigerated?
No. Odor Prints are POCR-based and need no special storage conditions. The only practical recommendation is a cooler ambient temperature and protection from direct sunlight, not refrigeration.
Q: Can I leave training aids in my vehicle between sessions?
Yes, as long as they're in sealed packaging and not sitting in direct sunlight for extended periods. There's no special vehicle-storage protocol beyond that.
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