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

Opsaks are a hoax. They are made of polyethylene, which is the same stuff that every commonplace ziplock bag is made of. They are more "odorproof" than regular ziplock bags ONLY because they are thicker. Doubling the thickness of polyethylene film decreases its permeability to small molecules by about an order of magnitude, so a polyethylene bag only has to be four times thicker than a regular ziplock in order to be 10,000 times more odorproof. Loksak, however, describes polyethylene as a "new-generation barrier film". Loksak also describes opsaks as "completely odorproof", despite the fact that this is not theoretically possible and they have failed several fairly rigorous tests (including one recently described in an article here on BPL).

There are real barrier bags that are made of multilayer materials that have far lower permeability to moisture, oxygen, and odor molecules than polyethylene. They are available in many different forms, including stand-up ziplock pouches which I find much more convenient than a flat bag for food storage. Actual barrier bags have been around for a very long time and they are used to package all kinds of common consumables, like coffee beans and grounds. These are readily available on ebay and various other places online, and they are also cheaper than opsaks.

> They are more "odorproof" than regular ziplock bags ONLY because they are thicker. Doubling the thickness of polyethylene film decreases its permeability to small molecules by about an order of magnitude, so a polyethylene bag only has to be four times thicker than a regular ziplock in order to be 10,000 times more odorproof.

This doesn't sound like a hoax to me… increasing thickness is a completely legit way to reduce permeability? which part is a hoax?

And from anecdotal evidence, I was amazed at how red thai curry can go through everything including a regular zip lock bag and it actually made my other food taste like curry. Yuck!

The opsack trick actually DID work but I stopped carrying curry because it was just too much of a hassle to cook.

Just try putting an esbit in an opsack! FAIL!

The "completely odorproof" part is the hoax. Real barrier bag materials are far more odorproof than polyethylene. Many companies manufacture or distribute perishable products that are vacuum packaged or packaged in dry inert gas (like coffee beans and many other foods). To serve these companies, there is a well established barrier bag industry. And they don't use polyethylene because it is a terrible barrier material.

I pointed out that opsaks are just thick polyethylene because Loksak calls it "new-generation barrier film", which is deliberately misleading. Loksak was already marketing cheap ziplock bags as specialized camera and phone protection systems when they had the idea that they could also market cheap ziplock bags as odorproof food storage systems. They claim that there is something special and technologically advanced about their bag material, and that it has special qualities that are unique to its advanced material (waterproof, flexible, transparent, etc.). They haven't tried marketing cheap ziplock polyethylene bags as high tech emergency floatation devices yet as far as I know.

Many people feel that it isn't worth it to use barrier bags because you'll just get food odors on the outside of them anyway. That's fine. However, I'm one of those (like you, it seems) who thinks that it might help, so I use one. And if I'm going to use a barrier bag, I don't see a reason to use one that is badly designed (bad material choice), overpriced, and produced by a company that attempts to mislead its customers.

So what brand do you use?

Any opinion on the Nylobarrier bags from LiteTrail?

http://litetrail.com/shop/litetrail-nylobarrier-odor-proof-bag

Since it sounds like you've done your research, any comments on the validity of "ASTM F1927 odor barrier tested" as a meaningful indicator of quality?

Nylofume bags are issued by termite companies to homeowners prior to the introduction of toxic gases. The homeowner double-bags food and then is permitted to leave it inside the house.

So, two layers of that is good enough to keep toxic gases from leaking inward. I would think that one layer is good enough to keep food odors from leaking outward. It kind of depends on the gas pressures inside or outside.

For example, if you seal up food at sea level and then carry it up to 14,000 feet, bad things might happen with pressure and odor leaking out. If you carry the food up to 14,000 feet and then seal it up in the bags, it would be completely different.

–B.G.–

I thought the BPL article on Opsaks pretty much cleared this up … or maybe not??? Maybe I'm missing something?

http://www.backpackinglight.com/cgi-bin/backpackinglight/odor_proof_bags_study.html

"Just try putting an esbit in an opsack! FAIL!"

Over two years ago I put 96 esbit cubes in an opsack (8 of the 12 pack boxes). They're still in there, except my supply has dwindled to about 48 cubes. There is also about 36 of the Coghlans emergency fuel tablets in there as well (started with 48).

There is not even the remotest hint of a smell coming from the bag, I even just put my nose right up to the plastic and gave several big wiffs…. but when I open it… phew! It stinks. I'm not saying they're completely odour proof, but carrying that many esbit cubes for a few years has me convinced that they at least keep "most" of the scents in.

The results of the Opsak bags published on BPL does not surprise me in the least, the only thing I find interesting is peoples response to the study.

I use foil stand up pouches I found on ebay. I just looked for them again and I don't see them now, but similar bags available from other sources online. They are made of a thin layer of aluminum foil (not vapor deposited Al) laminated to polyester film. They are stand-up pouches, about 10" x 14" when flattened, have a volume of about one gallon, and weigh 19 grams each, which is lighter than an Opsak of similar volume.

I don't have any well-informed opinion of the ASTM F1927 series of tests or any of the other standard tests used for measuring the permeance of oxygen, water, or other chemicals through films (ie, ASTM F739, ASTM F1383, EN 374, etc.). I think the polyamide material that Nylofume bags are made of is a much better choice than polyethylene, but the fact that the Nylofume material has been tested according to ASTM F1927 is not useful information unless we know the results. Also, the closure of those bags is not airtight.

I don't actually have a desire to discuss the minutiae of barrier bags in excruciating detail, and I feel bad about steering this thread off course. From my reading I have this simple understanding: a bag can't be meaningfully odorproof unless it has an airtight closure, and the ranking of bag materials goes roughly like this (from most to least odorproof):

1. Aluminum foil (usually laminated to polyester or polyamide film)
2. Aluminized (TVD) multilayer film
3. Aluminized (TVD) single layer film
4. Multilayer film (no metal)
5. Single layer polyamide film (no metal) <–Nylofume
6. Single layer polyester film (no metal)
7. Single layer polyethylene film (no metal) <–Opsak

So, I chose a foil ziplock stand up pouch, because that seemed like the best option.

Thank you for clarifying. My opsack bags did not work, I was very disappointed, they are not cheap. I had to put the esbit in the shed outdoors and away from anything I didn't want to stink like esbit.

I'm not on board with the consensus that the sack is at fault. Some smells are very persistent. Even stainless steel and plastic cutting boards can take on the odors of adjacent foods.

Soaking in liquid detergent is fine, but to get rid of odor, try a two-part soak:

1) in a vinegar/water solution

then

2) in a soda/water solution. (Don't combine into one soak, they'd cancel. Do it sequentially.)

Then ask your dog if he can still smell it. If he finds the sack interesting, it still smells, so then:

Wet some crumpled newspapers, leave them inside the sack, and leave it sealed up in the sun for awhile. Wet papers absorb smells.

Give it the dog test again.

Let me know if this works for you.

"I thought the BPL article on Opsaks pretty much cleared this up … or maybe not??? Maybe I'm missing something? "

The value of marketing …

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"m reading the BPL article now:

"Because the dogs were not trained to find salami or cheese, the “scent” for the study would consist of eight pouches of illicit substances used for the purposes of dog training"

I don't think this is a good comparison actually.

I don't carry cocaine in my backpack and bears don't exactly seek it out. There may be an issue with the molecular structure here that could bias the test one way or another.

A hungry bear (or dog) would be a FAR better test.

Anyone have a dog that they could experiment on? Maybe put food in an opsack and visually hide it from the dog vs a ziploc?

> The bags were then allowed to sit undisturbed for 30 minutes to allow scents to permeate the bags. During the study, a new pair of gloves was put on prior to handling any study bag to avoid cross-contamination.

this probably isn't enough time. 24-48 hours is probably a better comparison. Maybe even a week. If you use the same opsack over and over it has PLENTY of time to absorb odors.

Packitgourmet sells mylar-type bags quite cheaply — I'm planning to try those out very soon. And there is little doubt that curry is a "super-smell" food (there may not be ANYTHING -short of glass- that would block its odor!)

I was foolish once and decided to pack curry and make coconut red curry with instant brown rice.

BIG mistake. I had four days where EVERYTHING tasted like red curry.

Red curry granola bars. Red curry hot chocolate. Red curry honey.

It was horrible!

I have been very happy with my Opsack. Stored inside my Ursack I have yet to have any encounters with animals. Based on the feedback on this thread I guess that is just dumb luck.

Colin,

Where would Mylar fit in your ranking? A google search turned up a couple of possibilities:

http://www.ebay.com/itm/25-Large-8-x-12-x-4-48oz-Sliver-Foil-Stand-Up-Zip-Lock-Bags-Pouches-/261014883751

http://www.sorbentsystems.com/standupbags_order.html

Is this what you had in mind?

Thanks,

rhz

yeah.. dumb luck. I don't use one and haven't had a problem either.

reminds me of this simpsons quote:

Homer: Not a bear in sight. The Bear Patrol must be working like a
charm.
Lisa: That's spacious reasoning, Dad.
Homer: Thank you, dear.
Lisa: By your logic I could claim that this rock keeps tigers away.
Homer: Oh, how does it work?
Lisa: It doesn't work.
Homer: Uh-huh.
Lisa: It's just a stupid rock.
Homer: Uh-huh.
Lisa: But I don't see any tigers around, do you?
[Homer thinks of this, then pulls out some money]
Homer: Lisa, I want to buy your rock.
[Lisa refuses at first, then takes the exchange]

Ive been happy with the odor proofness. Perhaps the problem is that they are not the OP model, or that zipper closures are really tricky.

"yeah.. dumb luck. I don't use one and haven't had a problem either."

The dumb luck comment was me just being facetious. I have had no issues when others in camps around me have. I agree with Bob's comment that the closure system can be tricky sometimes and requires a fair amount of pressure to seal properly.

"So this is ironic… my opsack now smells like peanut butter and curry powder."

I think this must somehow be related to the immutable law of conservation of smell. I wonder, where do the smells go when they are proofed against? It seem unreasonable if not an outright violation of the laws of God and Nature, does it not, to demand that the smell BOTH outside and inside the opsack vanish.

I got some awhile ago but really have never had a chance to use them in the last few years. What would they be good for now other than trying to keep animals from smelling the odors?