The science of scent, bears, and ways to severely restrict odor diffusion

[Justin W]

Vacuum insulated panels (VIP’s) are made out of a composite of a few layers of plastic film with an aluminum foil sandwiched in between the plastic layers. Then there is a core, spacing, insulative material placed within, a vacuum is pulled to remove most of the air and during that it is sealed while under vacuum (there are also Getters placed in there to help absorb and/or adsorb moisture, oxygen, off gassed molecules of the plastic, etc). The highest quality VIP’s are rated for 50 years of useful life. This means that they can successfully almost completely limit the huge majority of gaseous exchange from within to without for a very long time (and under strong atmospheric pressure, pressure strong enough to break/splinter thinner, S glass reinforced plywood. Which I’ve done while doing some VIP making experiments). If they didn’t, they wouldn’t work. Vacuum insulation requires well, a vacuum, to work optimally.

The aluminum foil is doing the lion’s share of the heavy lifting in these systems. This is what prevents the huge majority of gaseous and moisture exchange. If there is no, or very little gaseous exchange, then there is also little to no scent being exchanged (scents need to be convected with and by gases to spread). The plastics on the other hand, well most plastics do allow some gaseous exchange over time (via molecular diffusion), as well as offgas some (there are a couple plastics that can hold vacuum much better, but they aren’t typically used in VIP construction for other reasons, like sealing/bonding issues. For example, PTFE).

With VIP’s, they do ultimately fail because there are micro to nano gaps between the plastic and aluminum foil layers, but I would say up to 50 years of holding a significant vacuum is pretty impressive.

What this means for bears and scents: If you use vacuum sealing bags with an aluminum liner, or mylar bags with an aluminum liner, and you properly use them, these would be much better than nylofume bags and the like for limiting scent diffusion.

The best practice would be to heat seal them, but that is not really feasible or practical in the backwoods. Instead, when at home, you use a little heat and a hard flat surface (like an iron), to fold over a few times, and then secure the last fold (with reusable tape, hook & loop/velcro, clips, or the like) this is the second best way of limiting odor diffusion. As long as the aluminum foil is tightly folded over itself a few times, it will be very hard for inside air to exchange with the outside air.

Again, by limiting gaseous exchange, you are also limiting scent exchange. A bear’s sense of smell is remarkable, yes, but operates within the bounds of physics. If a barrier is good enough for holding vacuum long term, then it is also very good for severely limiting scent exchange. It is really that simple.

Of course handling food and touching the outside of the bag will leave food scent on the bag. Pretty hard to eliminate that completely. However I wouldn’t worry about that. A bear’s sense of smell is so acute and their intelligence high enough, that they can differentiate between relative amounts–differences between residues (like on a used candy wrapper, or the outside of a touched odor reduction bag) and outright full meals/larger caches, and then run risk assessment. Why would a bear go investigate residual odors alone, unless it was starving/desperate? If they are under the latter condition, I wouldn’t worry too much about light, residual food smells, because then you’re potentially on the menu.

[David D]

The mylar versions (like Wallabys) also tolerate boiled water (unlike ziplocs) and are excellent to FBC in.

But they’re heavy.  I haven’t been willing to make the trade off of putting a week’s worth of food in them.

[Jerry Adams]

aluminized plastic bag with ziploc closure might work

20 Pack 1.5 Gallon Long Term Storage 6 Mil Thick (Each Side) Pound Mylar Zip Seal Bags. 12” x 16” Aluminum Layer, Food Grade, Smell Proof Pouch. Fits 1KG 3D PLA Filament Spools – Roypack

$20 for 20 bags 1.5 gallons from amazon

I just randomly selected that one, they have many, I don’t know if they’re any good

[David D]

Jerry, those are the ones we’re talking about. They’re pretty heavy though

[Jerry Adams]

how much does one bag weigh?

[David D]

A single Wallaby for one meal portion (7.5 Mil – 6.5″h x 8.5”w) is 20g

A medium freezer ziploc is 6g.  So I store dinners 1/ea in those, FBC in the Wallaby

[Jerry Adams]

If you only needed one of those to store your food that wouldn’t be too bad.  If it prevented a bear from discovering it would be well worth it.

[David D]

You’d need one per meal

Best case put each meal in a sandwhich bag and then some meals may be able to fit 2 per bag.  Probably still need 4 or 5 for a week (too heavy) and the sandwich bag would let odours cross polinate between meals.

A freezer bag per meal + one turkey bag or cut down nylofume or opsak for the lot and cook in a mylar/al bag seems the best compromise

[Justin W]

Just a quick note. If you want maximum odor blocking activity, unfortunately the zip loc style closing will not cut it. You really want/need the aluminum foil layer to be tightly folded over itself at minimum two times (more preferable).

If mylar bags are too heavy, I would suggest looking into the vacuum sealing bags that have a foil liner. In my experience with both, the latter seems a bit lighter than the big mylar bags. But I should probably look into that more deeply before stating anything definitive about it.

[jscott]

There’s always that moment when you need to cook and eat your meal. and then of course you and your companions smell like humans, and food. Bears know that humans carry food. Have a fire at night? Bears know that humans with food have fires.

It’s hard to imagine that at close range, a bear won’t be able to pick up the scent of a food bag. Maybe these bags make odors invisible to bears and they wander off flummoxed at finding humans out in the woods with no food…again, until you start cooking.

I use a Bearikade.

[Jon Fong / Flat Cat Gear]

Keep in mind that blocking odors can work very well. That being said, bear will also use visual clues to determine where the high calorie / high reward food items are. Seeing a foil pouch that is neatly sealed probably won’t deter a hungry bear. I have seen them run away with plastic grocery bags probably just due to association with food. It needs to be a complete system approach to work: I use a bear canister.  My 2 cents.

[Paul Wagner]

I work with an organization that installs and monitors wildlife cameras. The prodecures for these cameras are that you MUST wear surgical gloves to work on the cameras, because experience shows that even the slight residue of food on your hands after eating your lunch will provide enough odor to attract the bears and encourage them to eat the cameras.

So mavbe the container ain’t the only thing to consider here…

[Jerry Adams]

I would like to see the video of the bear eating the camera.  From the cameras point of view.

[Paul Wagner]

They have one.  The tech that installed that camera also got chewed….because the cameras cost a lot of money.

[Paul S]

I’ve used the mylar/aluminum bags for my #2 kit and esbit storage. Maybe not the intended used ;-) They function well — keeping the odors contained. They are a bit heavier than ziplocks and they tend not to fold up as small.

[Terran Terran]

I’ve seen gas cans mauled by a bear. They’ll investigate any and everything given enough time. However time is on your side. If they’re not socialized, they can be extremely cautious. Your fire won’t attract them.

[jj]

jerry,

https://www.youtube.com/watch?v=L2kRwqfVMKY

watch this video at around the 9:30 and 12:00 marks and you’ll see some bear interactions with the trail camera. I dont have time to look around but he has videos where the bears are much more curious. this one at least has some good panther footage in it too though

[Alan W]

On a multiday trail clearing project in Pecos W.A. of NM, we left various axes, Peavies, Pulaskies, crosscut saws, hard hats, and spray cans of PAM spray oil in a cache 30′ off trail at highpoint of work before returning to camp one evening.

Upon return the next morning, we saw that we would be crosscut sawing all day without any PAM spray and with 1 less hardhat.  The bear chewed into each spray can, apparently swallowing and licking with delight.

Lesson learned: no spray oil is left at end of day tool cache.

Over many years, we’ve not had a hung crosscut disturbed despite doubtless oil residue. Yes, visual cues matter also, depending on experience of individual bear.

[JG H]

I go a little over the top on mitigating scent and I don’t fret extra weight because I’d rather carry a few mote ounces than have a bear in my camp or end a trip early because my food ran off on four furry legs. I repackage my dehydrated meals into 4mil ziploc bags and I store those, plus solids and fragrant stuff, in odor-resistant ziplocs. Its not as glorious as foil-lined mylar or VIPs, but has always served me well. We backpack all over the Smokies, so it’s not like we’re in an area where bears are sparse, either.

[Jerry Adams]

Nice trail cam video jj

Bears licking camera, mountain lions, cute little ‘possum,…

[Jon Fong / Flat Cat Gear]

I hike in the Sierras and use Bear Canister.  I don’t seal my food in anything other than a ZipLok. I don’t bag liners in the can.  I cook spicy food and use a lot of aromatics.  I have never had bears mess with my Bear Canister, not even tipping one over.  They just walk past knowing that they aren’t going to get anything out of them.  My 2 cents.

[Philip Tschersich]

I would like to see the video of the bear eating the camera.  From the cameras point of view.

Like this?

[Jerry Adams]

Yeah, point of view of the inside of his mouth, looking out through his teeth, nice!

 

[jscott]

Notice the slobber on the bear’s lips as he approaches. that stuff is super sticky and nasty! And the main reason I won’t use an Ursak.

the point is, the bear is salivating heavily when approaching, wait for it, a trail camera! The operator ate some nut snacks when he handled the camera 12 hours earlier, and this is the result. don’t discredit the olfactory abilities of a bear.

[Terran Terran]

Never open your can and all will be good.

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