Long-term review: LOKSAK OPSAK || Food storage enhancer

Sunset in the Yukon Arctic. My food was stored in the clear OPSAK at the front of the shelter.

LOKSAK OPSAK bags are made of heavy-duty plastic and have a hermetic seal. When closed, the bag is airtight, waterproof, and odor-proof (the “OP” in OPSAK).

On some trips, I use the 12″ x 20″ size ($6, 1.5 oz) as a lone food sack or as a liner inside a wildlife-resistant Ursack. I also like the 9″ x 10″ size, which holds my daytime snacks and which I keep near the top of my pack.

The larger 12″ x 20″ size is ideal for storing multiple days of food. The smaller 10″ x 9″ is useful for daytime snacks, kept near the top of the pack.


LOKSAK OPSAK bags are tough, lightweight, and reasonably priced. Inside the 12” x 20” size, I can fit about five days of food. Less ravenous hikers can probably fit six.

The rectangular shape packs efficiently inside my pack, and its width fits perfectly a snack/sandwich bag, candy bar, and most energy bars. Because it is made of transparent film, the contents can be easily seen. The seal seems to blow out after 4-6 weeks, but I continue to use them for many months afterwards.

The width of the 12″ x 20″ Opsak is about the same as most candy/energy bars and snack/sandwich bags.

Recommended uses

On its own, an OPSAK is an inadequate method of overnight food protection. It’s best considered an enhancement to a more reliable method, by reducing food odors.

Most specifically, an OPSAK can be used to line an Ursack Major or Ursack Minor to make it less detectable or less interesting to a bear or rodent. Maybe that black bear two miles away won’t smell it, or maybe it’ll decide to visit a different campsite that is giving off stronger food odors.

My packed food prior to a trip in Glacier National Park, where Ursacks are allowed. My note says that I had 5 days of food in the Opsak and that it was “almost full.” I used the smaller 6″ x 9″ size for my daytime food.

If I’m using a hard-sided canister, I do not use an OPSAK as well. Canisters are not entirely bear- or idiot-proof, but I’m very confident in them as a standalone food storage method.

I never hang my food from bears, because I think other methods are more effective (e.g. canisters), or at least equally effective and easier (e.g. the Ursack Major). If you do hang your food, an OPSAK could add value to the system.

I will use an OPSAK on its own only if there is low risk (or, ideally, no risk) of bear or rodent activity at my campsites. And I will sleep with it — on it or immediately next to it, or keep it inside my shelter. I wouldn’t leave an OPSAK unattended even at “safe” campsites.

Is an OPSAK really odorproof?

Fresh out of its packaging, an OPSAK is both odor-proof and odor-free. After a few days of use, the OPSAK is probably still odor-proof (i.e. food smells do not permeate outside the bag), but I suspect its exterior becomes contaminated with food smells due to normal handling.

Bears have an extraordinary sense of smell — seven times better than that of a bloodhound, according to Yosemite — and I would imagine that this contamination puts the OPSAK on a bear’s radar. However, the food smell is probably no stronger than the food smell on your clothes or your shelter, and that level of food smell is generally not considered to reach the threshold for action. (Philmont would be a notable exception.)

To reduce food odor contamination, an OPSAK could be washed between uses with soap and water.

One 12″ x 20″ bag weighs 1.5 oz and holds about 5 days of food.


The transparent body material is heavy-duty and will withstand months of use. On my 6-month Alaska-Yukon Expedition, on which I used the OPSAK exclusively for food storage, I replaced them only twice (so two months per bag) and got several more months out of each bag on subsequent trips. Rips or tears in the body can be easily fixed with duct tape or Tenacious Tape.

The airtight seal has proven less durable, with an average lifespan of four to six weeks. After the seal blows out, I just close it up like a potato chip bag. I think this is “good enough” — if I thought that leaking food odors could make the difference, I should be using a more guaranteed food storage method anyway, e.g. hard-sided canister.

Holes in the bag body can be easily repaired with duct tape or Tenacious Tape. There is no fix for the seal, which I find blows out after about 4 to 6 weeks of daily use.

Do you have questions about or an experience with OPSAK bags? Leave a comment.

Buy now: LOKSAK OPSAK 12″ x 20″ Bag

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Posted in , on January 5, 2019
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  1. bart on January 5, 2019 at 8:33 pm

    Thanks Andrew for you honest thoughts on food protection.

    As always, OP sacks are not the solution in and of themselves.
    They’re a PART of the solution of a lower food odor signature.

    On the extreme end would be frying bacon or trout at the campsite.
    The other would be having freeze dried food in an OP sack inside a backpack.

    Of course I wouldn’t think that I could throw my bag of food in an OP sack into a bear cage, and they wouldn’t tear it apart. BUT, it’s like comparing what sharks do when you chum the water.

    I guess I get a month’s use out of an OP sack. So if you’re gonna walk 5 months, then have at least 4 bags for resupply.

    • Bart on January 6, 2019 at 10:52 am

      Oh, and I use the smaller OP sack to story my personal hygiene items.
      I use the smaller OP sack to store my trash.
      At night I’ll store those two items in the big OP sack.

      Agree on the seal. You’d think they would have fixed that weakness by now.
      It’s not the interlocking seal that breaks, it’s the plastic you pull to get the interlocking seal apart that fails. I would think the bag is still odor proof, but just a pain to open it.

  2. BCap on January 5, 2019 at 9:22 pm

    On the PCT where bear cans were not required we used opsack/ursack combo tied to trees/rocks nightly. Aside from a few mouse turds it never got touched. I call it a win for the opsack.

    • Andrew Skurka on January 6, 2019 at 12:17 pm

      Maybe. But what was the experience of other PCT hikers?

      When it comes to food protection, A/B tests are really limited. I think it’s fair to speculate that the OPSAK helps, but I’m uncertain that there’s any data to support it being more than speculation.

      • BCap on January 6, 2019 at 8:45 pm

        Quite a few PCT hikers we met had at least some rodent troubles, but there were a lot of possible reasons why that would be the case not related to the opsack. So, no negative control to speak of, but for the weight penalty and cost I’m fine with speculation and anecdote.

  3. Lagrandeimage on January 6, 2019 at 2:36 am

    Hello Andrew,

    How do they compare to Ziploc bags? The double closure ones seem good. Do you think OP-SAK has an advantage compared to those?

    Thanks in advance,


    • Andrew Skurka on January 6, 2019 at 12:15 pm

      Plastic bags, even heavy-duty freezer bags with a double closure, are not odor-proof. An OPSAK is made with a different type of plastic.

      If you don’t believe me, put some coffee in one and wrap it with a t-shirt or towel. After a few hours, the t-shirt or towel will smell like coffee.

  4. Max on January 6, 2019 at 3:10 pm

    Big one great with my ursack.

    I’ve used Smelly Proof brand small size ziplock style bags to house my super stinky esbit solid fuel system and that works like magic also.

    Wondering what bears think of that nasty rotten dead fish scent anyway?

  5. Bill Kay on January 6, 2019 at 3:36 pm

    Nylofume bags are odour proof and you can you use it as a pack liner. I have been using one as a pack liner for the past season and they seem durable. You could just get rid of the opsak and use the nylofume bags for both liner and odour protection.

  6. bart on January 6, 2019 at 6:37 pm

    Re Nylofume: Awesome! Thanks for that. Will change from compactor bags for that on this summer PCT.
    Freeze dried food inside a freezer ziplock bag…inside a OP sack…inside a Nylofume bag…inside a backpack…inside a tent….away from a high traffic campsite…away from a water source…
    Sheeze, there’s got to be a limit!
    If a bear can find me after all that…that’s one incredible bear. He/she DESERVES my food!
    Genes like that SHOULD survive.

  7. Bob S. on January 7, 2019 at 3:28 am

    I use food-quality, boil safe bags with my vacuum heat sealer for preparing sous vide precooked meals boiled right in the bag (no pot washing required). I also vacuum seal emergency supplies I don’t want getting wet.

    A package of 100 precut bags or an uncut roll for making larger sized bags can be purchased for around $15. The only drawback is this type of bag can’t be (easily) resealed in the field once you open it.

    The bags are super tough and reusable if you carefully cut just below the heat seal. You’ll lose about an inch off the bag with each use and I get 2 or 3 uses out of each bag depending on what I had in it. If I cooked turkey, stuffing, mashed potatoes, peas, and gravy in a bag I might only use it once but the bag only costs 15 cents and the food probably tastes better than the freeze-dried crap the guy on next island over is eating.

    I am usually kayak-camping on islands with no fresh water or bears of any size so this method of freezing, sealing, storing, and cooking food works for me. I would assume if the bag is tough enough to go from the freezer into a pot of almost boiling sea water for 10 minutes I would think food odors a bear could smell would not escape.

    Disclaimer: I have never bear-tested this storage method.

  8. bill on January 8, 2019 at 11:42 am

    I wonder if zipper mylar bags would be more durable and comparable in weight. they’re food safe and odor proof.

  9. Bryan on January 10, 2019 at 10:59 am

    I am going to be trying these this season, https://smellyproof.com/ they are cheaper, come with a pleated bottom (one thing I dislike about OPSACKS) and many sizes. As are supposedly bear tested!

    • ginny on January 11, 2019 at 4:47 am

      Those smelly proof bags seem like a good option–wonder if they work with minibears too? Would love to have Andrew’s opinion on them.

    • Bill on January 11, 2019 at 5:27 am

      They seem like a really good option. Thanks for sharing.

    • Gary on April 26, 2019 at 6:33 am

      I use Smelly Proof bags, and they’re perfect. I’ve used them in Yosemite and also outside of bear-country, and I’ve never had an issue with other critters. Haven’t tried any other options, but I haven’t had a reason to yet.

  10. Kate on January 29, 2019 at 9:29 pm

    I’ve just purchased some Opsacks and Loksacks for a trip. I’m reinforcing the tops with packing tape before I start using them. It’s the kind of tape that looks like gift wrap tape, but much sturdier. We’ll see how that goes.

    I like the sound of those Smellyproof bags – seems like a much more practical form factor.

  11. Pliny on May 18, 2022 at 2:39 pm

    Very interesting. I did a little research and sniff dogs can detect even the most carefully packaged dope. And bears have an even much better ability to smell scents than dogs. Wow. One of the many problems the drug smugglers encounter is that undetectable dust from the produce drifts into the air in the room where you are packaging it and after packaging gets on the o/s of the package. The more I read the less likely fooling an animal that makes it living smelling scents seems. Not that we shouldn’t do our best. My food is individually wrapped in saran wrap, in a zip lock bag, in a 16-gallon kitchen garbage bag. We have lots of bears here, but fortunately, they have never bothered us in all my years. We do hang our food at night, but never any evidence of any animals larger than a chipmunk around our food. https://hightimes.com/news/laws/trick-drug-sniffing-dog/

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