My scumbag opsack is now putting out an odor! :-P

"I bought both the odor proof bags and the pack liner. Each one developed punctures on their first use (and I am not rough on my gear at all)."

I can't speak to the pack liner, but I have used Nylobarrier bags several times each
and they are still puncture free. For me the technique is to use them as a liner for a stuff sack, which can then be used to hang my food when in bear country. The stuff sack protects the Nylobarrier bag from abrasion, punctures, etc. I wash them between trips, and they are then good to go for the next one.

Rafi, the bags in that ebay listing look similar to the bags I use (but smaller). The Sorbent Systems page has bags of many different kinds, though.

This year marks the third time opsaks were used for caches in Colorado wilderness areas. This year for over a week, and the cache remained untouched. There was also the test in the national forest near home, mentioned in a post on the BPL article, with the link to the thread.

Clip'n seal clips or the like from Amazon are essential with opsaks to insure that the seal is tight.

On all three occasions, a week's food for moi and 2 dogs was double bagged in opsaks,
clip'n sealed, and 4 bags were placed in a coated Spectra Ursack (the green ones – no longer sold) and hung about 20 feet high. If a bear did smell it, it would be easy to get down, but they are hung to avoid being moved by lesser beasts.

When unpacking opsaks, the odors are very strong, as they are trapped in the sacks for long periods. So, yes, they smell a lot.

While BPL has a long history of superb test articles, the one on opsaks was total nonsense.

Would almost like to see one of the caches fail at this point, just to raise some question … but only almost. As earlier noted, opsaks would probably not work very well for carrying food, as the repeated removal and replacement of food in the sacks would contaminate their exterior with odors. But for caches, no failures yet.

Or maybe the bears have all left the Colorado wilderness areas, and I am way off base.

You hung your food 20 feet up, later found it intact, and so decided that Opsaks are odorproof.

If I did your test, (hanging food-filled Opsaks 20 feet up for a week and later finding them intact) and then decided that this means that Opsacks make things invisible, what would you say about my conclusion?

I'm glad that your food cache was untouched, and maybe Opsaks are odorproof and they are the reason. But you didn't test the odorproofness of Opsaks.

I'm curious about your opinion that the locker room test described in the BPL article was nonsense. I don't see it that way, but I'm willing to learn.

Yeah,

I hung a Opsack from a Joshua Tree and no bears got to it. Must be odor-proof.

I like the method of the original dog-test, given the short time and other limits.

Colin,
Methinks you read too fast.
The caches have been used now for three summers in three wilderness locations, not to mention the test in the forest at home (we have lots of bears).

As for the article, the basis for my opinion was posted there at length for anyone who wishes to read it. The link to the thread about the home test was also provided.

Hume was a great philosopher, but at some point, if the pool ball keeps going into the pocket, you have to give credit to the player.

Samuel, I don't know where to start. I agree that testing the function of something in a lab (or a locker room) is not the only way to learn about it. Testing under more realistic conditions is useful, if those tests are planned well. In my opinion, the tests you did were not planned well and they don't show what you think they show.

This is my understanding: you have used Opsaks for storage of food caches for up to a couple weeks and an animal has never breached one. Also, you did a test in which smelly foods were hung in bags and an animal got into the one that had no Opsaks. In that test the bags were arranged like this:

Where the box is the smelly stuff, the red are the ziplocks, the black are the Opsaks, and the green are the stuffsacks. Is this right?

Colin,
Nice diagrams. They seem about right.
How many treks would I need to successfully use the Opsacks for caches before you think them worthwhile? Just wonderin'.

I'm convinced. I'm convinced that what you're doing is working. If I was going on a trip with you I would ask you to put my food with yours because you seem to have found a good method.

I share lab space with a colleague who does a lot of isolation and identification of parasites. And, like you, her methods always seem to work. I recently developed a new method for isolation of parasite cysts and oocysts from water samples, and she and I compared the new protocol with her standard protocols. We did each of them together. As we went through hers, I asked questions about why she did things the way she did. Some of her answers didn't make sense. She insisted on using test tubes of a certain color, and arranging supplies on the benchtop in a certain way, and doing the work at a certain time of day, because ever since she started doing it that way it has ALWAYS worked. It was superstition.

I think something similar is going on with Opsaks. Suppose a person has twenty years backpacking experience, and they have hung 3000 food bags from branches in that time. Thirty of those (1%) were damaged by animals. Then, that person acquires an Opsak/Nylobarrier/Ursack/RatSack/etc. and uses it for 100 food hangs over two years. No animals get to the food. If that person is like most of us, they will be convinced that their new tool (Opsak/Nylobarrier/Ursack/etc.) is wonderful and it must do exactly what the manufacturer claims (odorproof, toothproof, etc.). This person will become convinced of this after 100 nights (maybe after 10 nights) even if, in the past, they had numerous stretches of 100 consecutive unbreached food hangs without the new tool.

Ari's locker room Opsak test was well designed and executed. Your objection that it lacked odor-free negative controls is wrong (the dogs checked for pre-existing scents like foods before the test), and the difference you allege between drug dogs and wild animals is also wrong (not substantial or relevant). In contrast to Ari's decent (but not perfect) test, the tests I've read about that purport to show that Opsaks are odorproof are so bad in so many ways that I don't know where to start assessing them. Your test, for example, does not at all test what you think it tests.

First, you compared the Opsaks to nothing, not to ziplocks (because both bags had ziplocks). This is not valuable. Wrapping an odor packet (composed of food in ziplocks) in wet newspaper or dollar bills or band aids is also better than nothing. This says nothing about Opsaks. It just demonstrates that, given two choices, an animal will be more attracted to food that is wrapped in fewer layers.

Second, you tested preference, not detection. The animal might have detected both but chose the smellier one; it might have eaten from the Opsak one if it had been the only bag there. The animal left food in the bag it raided, so it might have chosen not to breach the Opsak bag because it was full. Ari's locker room experiment tested detection.

Third, because n=1, the animal might have just eaten from the first bag it came to, as far as we know. This problem is the reason that good experiments have larger sample sizes. And twenty experiments each having a sample of n=1 do not equal one experiment with n=20. A lot of n=1 experiments that can't prove anything do not add up to one big experiment that proves something.

Fourth, I'm not sure that the question that your test sought to answer is a question that anyone is asking. Opsaks are clearly better than nothing and they are almost certainly better than one standard ziplock because they're made of the same material (polyethylene), just thicker. Opsaks are just thick polyethylene bags with crappy ziplock closures, despite claims by Loksak that they are a "completely odorproof" "new generation" material.

My claim is that Opsaks are much more expensive and no better than multiple standard ziplocks, and, if a person really wants to try an odor barrier, it makes much more sense to use a real barrier bag (like those described earlier in this thread), which are cheaper than an Opsak and orders of magnitude more odorproof than an Opsak or many standard ziplocks.

All we want is a method that performs well, and you have that. I think you should be happy with your technique. My point is that, in the long run, it can prove useful to know why something works. It is impossible to improve something (by eliminating unnecessary parts, for example) if our understanding of its function is superstitious.

Colin,
Appreciate the great deal of thought you have given to this issue.
You again commented to the effect that "Your test, for example, does not at all test what you think it tests."

I'd like to see whatever I said that suggested what you think I think I was testing. I try to make zero pretense on this site at any kind of scientific training, even to the extent of frequently commenting on my lack of it. A concern arose on reaching the age and physical condition where caches became essential for longer treks. So the desire was to see what would happen in two identical situations if Opsaks were added in one and not in the other.

Your lab partner may be superstitious or prone to unnecessary protocol. That is very common in many professions, and I run into it all the time, including with myself. But whatever her issues may be, you should not paste me with it. She is she, and I is me.

I've never been much of a bear bag hanger, except once when I wanted to impress a lady who was packing with me. Just lazy, or tired after packing all day, I guess.
But leaving a bag out alone by itself for over a week is another matter altogether. When this became necessary, I wanted some reassurance before using the caches, and risking a ruined trek. I posted here exactly what I was going to do, and there was not one whiff of a suggestion by anyone about how it could be done better. So I proceeded, and you know the rest. Except that after the no-Opsak bag was twice raided, it was removed and the Opsak bag left up alone unmolested for a month or so. I later updated the thread to that effect. And when I said we have lots of bears here, I meant it. Bears come from the forest into our back yards whenever there is any food around. My neighbor had a dumpster that the bears couldn't get into, but they hung around at night constantly, so he finally had to get rid of it. We have to keep trash containing any trace of food in our basement until it goes to the landfill.

Your comments about the bags being the same material, with some just thicker, are not supported by any evidence. From common experience, I know that plastic bags are made of a multitude of materials, with varying resistance to penetration by water, odors (gasses), etc. If there's more out there about the Opsaks being the same material, please post about, if you have the time.

As for Ari's dogs, I read the article carefully, and did not see documented the rigorous pretesting that you refer to. He says it was a concern, but very little about what was done about it. As earlier noted, those lockers could have had any number of things in them at an earlier time, not to mention how the dogs' could have been affected by their earlier training. Again, the best way to deal with this is to make the test as true to life as possible, and the article did just the opposite.
However, I suspect from your posts this is one issue we are not going to agree upon, and it may well be wisest just to accept that.

Agree that the LiteTrail bags are worth a shot, but not before I see what the local bears do with them. If you have some simple ideas how that can be done better, please let me know.

What concerns me a bit is your determination to take issue. It makes me wonder if this is more about ego gratification than truth-finding. There is a lot of that on this site, way too much IMO. Fortunately, most are OK with expressing their opinions and accepting that others feel differently. I guess that's what we probably need to do in this case, assuming we are both capable of it. Some are not. That's life.

It goes without saying that we appear to disagree. We each recognize and accept that, I assume. I see no harm in disagreeing, and I also see no need to run from it. A good debate can bring interesting information to light and improve one's understanding of a topic. Given your long and numerous posts, it seems that, like me, you are interested in this topic. The decision to participate is yours.

"Your comments about the bags being the same material, with some just thicker, are not supported by any evidence."

Debating things that are obvious isn't interesting to me. Please just read the Loksak website. They explain that Opsaks are made of polyethylene, including this sentence: “These resealable, washable, polyethylene bags are watertight, airtight, and odorproof, so they prevent animals from sniffing out your edibles and toiletries." There are, as you say, many different kinds of plastics. But commonplace ziplock food storage bags are polyethylene, and they are clearly thinner than Opsaks. This is common knowledge and easy information to find.

"As for Ari's dogs, I read the article carefully, and did not see documented the rigorous pretesting that you refer to. He says it was a concern, but very little about what was done about it. As earlier noted, those lockers could have had any number of things in them at an earlier time…"

I think this criticism of yours seem poorly thought out. In the article about the locker room study is this sentence: "Prior to beginning, one dog and handler team conducted a locker-room search to rule out the possibility of drugs on site that were not part of the study." So, any pre-existing odor that might throw the dogs off would have been identified before the test. However, drug sniffing dogs are specifically trained to overlook all non-drug odors. People commonly attempt to use other odors to conceal stashes of drugs, and the dogs are trained to not be distracted by those. The dogs were only looking for the odor of the material in the test bags, which is ideal for testing the odorproofness of the bags. Also, you have to choose between complaining that this test had too many complicating circumstantial factors and complaining that the circumstances of the test didn't have enough realistic complexity. Wild animals seeking food are surrounded by lots of other odors, too. And, like the drug dogs, the odor they are trying to pick out from the background odors is the odor of the stuff in the bag.

There are a few points that are obvious. This information is available from many sources online and I'm not interested in debating it:

1. Opsaks are made of polyethylene

2. Polyethylene is an abysmal odor-barrier material compared to nylon, metallized plastics, and foil.

3. In some industries it is crucial to have effective odor barrier materials. Companies in those industries don't use polyethylene because, compared to other materials, it isn't an effective odor barrier.

4. Real barrier bags are cheaper than Opsaks but similar in weight.

This is all we need to know. If you doubt any of these, please just look them up.

This in no way means that anyone using Opsaks should replace them. As your test results suggest, they are better than nothing. And your food cache experience shows that, for you, they work well enough. I think anyone who is using Opsaks now, and having good results, should continue to use them and not worry about this topic.

This is my only claim: if one is considering acquiring an odor barrier bag, it doesn't seem to make sense to consider Opsaks, because real barrier bags are cheaper, similar in weight, and made of materials that are better barriers. If you disagree with this statement, you are welcome to explain why.

Colin,

A good debate is OK, but there a "few" points you're not interested in debating, hah-hah.

But I think your posts are valuable in suggesting alternatives. Although you do not name them, several other posters mentioned the NyloBarrier bags form Lite Trail, that are much less expensive, larger, and a lot easier to use than Opsaks. Frankly, the Opsaks are a pain in the neck, just not as big a pain in the neck as arriving at a cache in a remote area after a week of hiking, finding bears got to the cache that was to provide food for the next week of packing, and having to bail out. I've not yet had to bail out for this reason, but have for other reasons, and it was an incredible bummer.

So next spring, when our bears come out, I will return to the small clearing in the forest behind the house and see how the Nylo bags do next to the Ziplock freezer bags used before. Can't wait to post the results. Note: The Ziplocks now have double sealing strips.

Would be interested in any suggestions you might have for the test.

"I will return to the small clearing in the forest behind the house and see how the Nylo bags do next to the Ziplock freezer bags used before. Can't wait to post the results."

Excellent! I will very much look forward to hearing your results. One suggestion, if you haven't already thought of it: After putting your food in the Nylobarrier bag and sealing it, wash your hands thoroughly and then seal the first bag in a second one to eliminate the possibility of scent traces on the outside of the first bag attracting animals. This is SOP for me when I am in serious bear country.

Samuel, I'll give it a little thought. If I have any ideas for your test, I'll send them along.

By the way, I should mention that disagreeing with you has been pleasant, thanks to you. Contention can take the fun out of a good debate, and make it unproductive, but your good natured posts (despite my occasionally abrasive tone) have made for an enjoyable discussion. It is appreciated.

I think the article was well written and proved without a doubt that the bags are not completely odor proof, but I don't feel like the article addresses how useful "odor proof" bags are for their intended use.

The intended use of OP bags is to prevent the smell of food from attracting wild life. I strongly feel that when properly used OP bags reduce the amount of smell to the point that it would not peak the interest of most wild life. Animals don't track down miniscule amounts of smell because there is no food reward associated to tracking down those scents.

Drug dogs on the other hand are TRAINED to sniff out miniscule amounts of scents and are rewarded with food, play, being petted. Of course they are going to pay attention to the most miniscule amounts of scent and focus on tracking it down because they have been trained to associate following those scent trails with receiving a reward.

Don't go swearing of your OP bags just yet. I use the nylobarrier bags inside a stuff sack. Every once in a while I get home and I don't sort out the last bits of my food bag for a day or two. My pitbull who has chewed through a suitcase to get to an un-opened summer sausage has never payed attention attention to my food bag.

-Loki

"Debating things that are obvious isn't interesting to me. Please just read the Loksak website. They explain that Opsaks are made of polyethylene, including this sentence: “These resealable, washable, polyethylene bags are watertight, airtight, and odorproof, so they prevent animals from sniffing out your edibles and toiletries.""

You piqued my curiosity, so I followed your recommendation and did some reading over at loksak.com. Here is what I found: "Our new Odor-Proof barrier bag, OPSAK, has all of the features of the aLOKSAK PLUS A NEW-GENERATION BARRIER FILM THAT IS COMPLETELY ODOR-PROOF."

I capitalized the relevant phrase for the sake of clarity, as it is apparently easy to overlook. The clear implication is that the OPSAK is composed of 2 layers, one polyethylene, and a film made from an undefined(proprietary?) odor-proof material.
This would certainly seem to at least partially explain Samuel's results. This is not to say OPSAK's are the best choice, by any means. I gave up on them last year, as soon as NyloBarrier bags became available, primarily because of the finicky, unreliable zip lock sealing mechanism.

Tom, the implication you inferred from that quote is not as clear to me as it is to you, but it would be interesting if it came to light that Opsaks are a multilayer film. The Opsak material is soft and subjectively it appears to be a monolithic polyethylene film. So, if it is a multilayer film, it is a pretty safe bet that it doesn't include a PET (polyester) or PA (nylon)layer (which are "hard", crinkly, low elongation materials). The only "soft", high elongation materials I know of that are used in barrier films are PVA and PVDF. PVDF, however, is naturally a milky, translucent color when dry (it turns clear when wet), and Opsaks are clear. That leaves PVA.

As long as we're on trivia, I'd note that even a multilayer film will never match the barrier properties of metallized and foil bags. Small molecule permeance for foil bags is typically 1000x lower than the best multilayer clear films. This is why some barrier bags are metallized on one side and clear on the other, or even metallized all over with a small clear window; companies want buyers to see their product but they want to maximize the proportion of the bag area that is metallized in order to minimize permeation of oxygen, water, and odor molecules.

"Tom, the implication you inferred from that quote is not as clear to me as it is to you, but it would be interesting if it came to light that Opsaks are a multilayer film. The Opsak material is soft and subjectively it appears to be a monolithic polyethylene film. So, if it is a multilayer film, it is a pretty safe bet that it doesn't include a PET (polyester) or PA (nylon)layer (which are "hard", crinkly, low elongation materials). The only "soft", high elongation materials I know of that are used in barrier films are PVA and PVDF. PVDF, however, is naturally a milky, translucent color when dry (it turns clear when wet), and Opsaks are clear. That leaves PVA."

Not to be overly disputatious, but when they say "plus" a new generation barrier film(definition: a thin skin or membranous coating) it sure seems to indicate another layer is involved . I suppose the best way to resolve the issue would be to email the question to loksak, but I'm not sure I'm that interested in pursuing the subject further. As I mentioned earlier I'm no longer using OPSAK's, so this discussion is purely theoretical for me. As for the rest of your post, given your use of words like "subjectively" and "it's a safe bet", I'm left to wonder if perhaps there have been advances you are not aware of in the materials you mention that would alter their textural properties. Or perhaps there are even new materials you are not aware of. They did say "new generation" after all.

"As long as we're on trivia,"

The devil, as ever when it comes to the real world, is in the details. As any scientist is well aware ;0)

I'd note that even a multilayer film will never match the barrier properties of metallized and foil bags. Small molecule permeance for foil bags is typically 1000x lower than the best multilayer clear films. This is why some barrier bags are metallized on one side and clear on the other, or even metallized all over with a small clear window; companies want buyers to see their product but they want to maximize the proportion of the bag area that is metallized in order to minimize permeation of oxygen, water, and odor molecules."

A multilayer bag construction involving a film doesn't have to match the barrier properties of a foil/metallized bag, although in the absence of data driven comparisons I'm not inclined to accept your statement as a given. All it has to do is fool the bear. There are probably several ways to skin this particular cat, one of which is no doubt metallized bags, but another of which may well be some form of multilayer bag with an odor proof film. BYOB would seem to be the order of the day.

http://litetrail.com/collections/sale/products/litetrail-nylobarrier-pack-liner

"seconds"

Also, my personal OpSak test with my, and a few friends dogs resulted in essentially the same results as the BPL test. They could smell the difference, with new bags, and especially more used bags, between the bags with the treats they love vs their standard dog food.

All this said, regardless of how odor permeable the material is, the outside of the bag will end up taking on a smell, your bear bag itself will take on a smell, etc. So what you are doing is not attempting to prevent any smell from emanating, but to minimize the smell to where the bear will decide to go to other smells first, or not be able to smell it from the distance they happen to be. At that point, they will smell your body well before they will smell the bag. If they decide to approach because of your smell, they will find the food regardless of what you put it in.

Bags like this just buy you one more level of comfort so you can sleep at night, they don't buy your food 'bear invisibility'.

From earlier in this thread: "So next spring, when our bears come out, I will return to the small clearing in the forest behind the house and see how the Nylo bags do next to the Ziplock freezer bags used before."

OK, so this is what happened. First, please note that nobody sent me any suggestions, protocols, or the like. If you do PM me, please include an email address if you'd like a reply – my PM service receives but does not send.

Three bags were hung on April 7th, when snow was still on the ground, at the same forest clearing used before. Dark olive nylon bags from Walmart were used for hanging. The food used was birdfeed, "Wild Berry Treat" consisting mostly of suet, and some canned salmon and canned sardines. The food was placed inside 3 freezer pint Ziploc bags. One Ziploc was placed inside an Opsak, one inside a Lite Trail Nylo Barrier Odor Proof Bag, and one remained naked. The Opsak, Lite Trail and naked Ziploc were each sealed and placed inside one of the 3 nylon bags. Here are pix of food stored only in a naked pint Ziploc, and in a pint Ziploc placed in a sealed Opsak. The pix were taken later after final removal of the contents from the nylon stuff sacks:

On the left is the food in a pint Ziploc, stored in a medium Opsak with a Clip'n-Seal cllp, and on the right is the food stored in a naked pint Ziploc. There is no picture of the Ziploc pint bag and food that was stored in the Lite Trail bag, as that was 'taken.' However, the Lite Trail was twisted tightly shut and tightly secured with each of the two twist ties provided, an inch or so apart from each other.
(No instructions came with the Lite Trail bags.)

The bags were hung from tree limbs approximately 50 feet apart, all with the Walmart nylon bags as an outer cover. After several weeks – nothing. After several more weeks – nothing. So on May 15th, the bags were moved to a more remote location where in the past, hunters had placed a bear stand for several seasons. The snow was long gone by this time and ticks abounded.

The three bags were hung 75 to 100 feet apart, and suspended about seven feet high from branches 25-30 feet high that were judged too light and springy for a raccoon or the like to walk out upon and pull up the cords. The area was accessed from a nearby game trail, identified by moose and coyote tracks often seen when snowshoeing. The Lite Trail was closest to the game trail, but at least 100' from it, the Ziploc around another 75 or so feet away, and the Opsak another 100 feet or so away. The distances are only approximate and were not equal, as the primary goal was to find high hanging branches that would support little weight, but would not break, and they were scarce.

Several more weeks passed. We're in early June now. Nothing. So the bags were lowered to five feet. One June 21st, the nylon bag containing the Lite Trail bag was found on the ground ripped open, with the Lite Trail bag ripped apart, and the Ziploc containing the food was gone without a trace. Here's a pic:

The Opsak bag, furthest from the game trail, was also found on the ground, with the cord cleanly severed right at the top of the outer nylon bag; but there was no sign of damage to the nylon bag, and the Opsak, Ziploc and food inside were untouched. The nylon bag containing the naked Ziploc with the food, that had been hung between the other two bags, was found still hanging, apparently untouched, still at five feet above the ground. Here are pix of the nylon bags containing the Opsak and Ziploc bags after they were recovered:

At this point, I felt not much could be made of all of this, so retrieved all the bags. The odor from the naked Ziploc bag was strong and foul, and could be smelled right through the bag. Not so with the Opsak. The torn remains of the Lite Trail bag was all that was left in its nylon outer bag, and the Ziploc with food was gone without a trace.

But I did draw one conclusion and a couple surmises form the above. First, I would not trust a Lite Trail bag. Also, I do not think bears were involved, and suspect coyotes were at work. We know they are around because they make quite a racket celebrating after each kill. And I would think bears would have done more damage to the nylon bag containing the Lite Trail. Lastly, I don't think the survival of the naked Ziploc shows much, as the Ziploc inside the Lite Trail bag didn't help it much, and the naked Ziploc stank when retrieved. Of course, you are free to draw your own conclusions.

A little daunted by all this, I have been in contact with an acquaintance who works at a bear shelter, and am hoping to obtain some more reliable tests of the bags next year. Next time, I will probably double bag, as that is what I do when using the Opsak bags for caches. (Note: The Opsak bags now come in a larger size that better fits the clip'n-seal clips.) If anyone has any suggestions about protocols, I remain open to them. Possibly, the bags could be placed well apart from each other on the tops of a bear enclosure to see if any bears are attracted to them. In that way, the bears would not receive the food, with the negative consequences that might entail.

Thought you might be interested, so there you have it. Sam in Chocorua.

Thanks for going to the trouble of carrying out this test, Samuel.
Unfortunately, it would seem that the test has failed, since the control bag was untouched, so we can't really conclude anything from it. The fact that the Opsak bag was uncompromised COULD be that the animals were disturbed before getting at the food.
Incidentally, the nylofume bags are supposed to be used double bagged (for fumigating) and I would suggest anyone doing further testing try them double bagged.

"Incidentally, the nylofume bags are supposed to be used double bagged (for fumigating) and I would suggest anyone doing further testing try them double bagged."

+1 SOP for me in the backcountry.