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Keeping your food safe from wildlife is an important consideration on any camping trip, and assumes even greater importance when traveling through bear country. Historically, options for food protection have included food hangs and bear-resistant canisters or sacks. Food hangs or “bear bagging” can be technically challenging, requiring that the food bag be suspended at least 12-15 feet above the ground and 8 feet from the trunk of nearby trees. Bears frequently foil these hangs by climbing out on the supporting branch to access the food, or by breaking the branch off using their body weight. Bear canisters are highly effective at deterring hungry bears, but do not prevent them from being attracted to the campsite. Additionally, these canisters can add considerable bulk and weight to a backpacker’s load.

Learn about bear canister use, design, and performance in our latest BearVault 500 (BV500) Review.

How Safe Is Your Food? Investigating the effectiveness of odor-proof bags - 1

In recent years, a number of odor-proof bags have been marketed with the backpacker in mind. These are typically made from heavy-duty polyethylene or nylon polymer and are advertised as waterproof, airproof, and odor-proof. Odor-proof claims are apparently derived from anecdotal experiences, testimonials, and tests of oxygen gas transmission rates through the plastic film that the bag is made of. An extensive Internet search did not turn up any unbiased scientific studies evaluating the effectiveness of these bags in preventing odor transmission.

How Safe Is Your Food? Investigating the effectiveness of odor-proof bags - 2

As an emergency and critical care veterinarian at a university hospital, I’ve gotten to know some of the officers in K9 units pretty well over the years. One day, I was talking to one of the officers, and the conversation turned, as it often does, to ways that people have tried to outsmart the dogs using a variety of scent masking strategies. Strong odors like coffee, “scent lock” hunting products, and even concealment in sealed steel containers had proven no match for the dogs. I asked about odor-proof bags. The officer had never heard of them but was more than willing to put them to the test. And so, the idea for a study was born.

Based on manufacturer claims that the bags were 100% odor-proof, we hypothesized that the odor-proof bags would prevent dogs from detecting substances hidden within, or at the very least would greatly delay their identification. To test this hypothesis, we planned to run a series of timed searches for scent pouches hidden within odor-proof bags1. Ordinary supermarket ziplock bags2 would be used for the control group. 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 dog training. These would be divided between the study groups such that each of the four odor-proof bags would have a matched ziplock control containing a similar type and quantity of scent. Four police dogs were available to participate in the study, and each would perform searches for all eight of the study bags for a total of 32 searches. For data analysis, we would compare the number of bags found in each group and the average time it would take for the dogs to find the bags, if they could, in fact, find them.

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Study Design

We conducted the study in the women’s locker room at the university. This was one of the largest rooms available, and the uniform rows of lockers would allow the bags to be concealed without visual clues for dogs or officers. Because some of the lockers had locks and others did not, we put ‘dummy’ locks on a number of the lockers used in the study to ensure that the officers would not focus their dog’s attention on only unlocked lockers.

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Four odor-proof bags and four ziplock bags were prepared as described above. Bags were numbered from 1-8 for identification purposes. To avoid transferring scents to the exterior of any bag, one gloved investigator held open each bag while an officer dropped in the scent packet. The bag was sealed and handed off to a third person to check the seal. 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 before handling any study bag to avoid cross-contamination.

Before 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. This step concerned me during study design, and I was greatly relieved when it was over. No students were implicated in the making of this study.

Study bags were now hidden two at a time, each in their own aisle, and allowed to sit for 5 minutes to establish a scent trail. One dog was then brought in and instructed to search. Dogs were timed from the initiation of the search until they definitively signaled a find. They then moved on to the next aisle to search for the second bag. The officer was permitted to terminate the search if he felt that the dog had adequately searched the aisle and would become frustrated if forced to continue.

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It was anticipated that the longer the drugs sat, the more scent would permeate the bags, potentially making them easier to find. Consequently, bags were presented to each dog in random order to avoid giving an advantage to any particular bag. To minimize the effect of study bag location on search duration, the locker room was divided into two zones, zone 1 (10-30 ft from starting position) and zone 2 (40-60 ft from starting position). Each odor-proof bag and its respective control (the ziplock bag containing the matching type and quantity of scent) were hidden in the same zone.

How Safe Is Your Food? Investigating the effectiveness of odor-proof bags - 5Officers were blinded to the contents of the lockers to avoid having the dogs look to them for cues. After each successful search, dogs were rewarded with their favorite toy and taken from the room. The study bags were removed from their lockers, and the doors were left ajar to minimize confusion due to lingering scents. The room was then reset for the next search. This strategy of swapping lockers and study bags between searches, as opposed to having the dogs search for each bag in the same location, was implemented at the recommendation of the canine handlers to avoid the possibility of one dog following another’s scent trail to the bags.

How Safe Is Your Food? Investigating the effectiveness of odor-proof bags - 7

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