I've tested it with my sole remaining dog. Well, actually, my wife's new puppy. Like all growing pups, he's a real "chow hound".
I've tried both cheese and peanut butter, and his favorite bacon scented chew (the bacon scent is so strong, i can smell it faintly just entering the kitchen.
First, the pup is placed upstairs out of "earshot". The pup, just 5mos old, already associates the sound of all types of noise related to plastic bags with food.
Then, a two person assembly job. I never touch the foodstuffs or chew. She doesn't contact the zips. My wife places each of them in a Glad zip-lock bag. Then, each of the two zips are placed in an O.P. Sak purchased on the BPL website some many months ago.
O.P. Saks are placed in dining room. Pup eventually finds them as he wanders about (plastic odor??? or serendipity???). The pup is curious, sniffs, and ignores the O.P. Saks.
Now the Glad zips are removed from the O.P. Saks and placed in a freezer sized zip-lock bags. The test is repeated. Bags are placed in dining room.
Pup finds the bags and bites at the bags.
Need to do the test in this order since a dog (and most animals), when it comes to food, can learn to associate (probably not a memory in the human sense of memories, hence the term association) from a single exposure/experience. That is, to be a little clearer, if the test is done the other way around, a dog, the pup in my case, would be attracted to the O.P. Sak simply because it had already learned or associated food with plastic bags.
Richard, i've had dogs for years and though an amateur have much experience training dogs - both mine and friends. I would also kennel friend's dogs at my home, where they all would receive some obedience training even if that wasn't the purpose for the stay.
Training for my dogs consisted of on and off lead obedience - both verbal and non-verbal (i.e., hand signals), out-of-sight whisper commands like used with sentry dogs in Viet Nam, protection, tracking, and now therapy-dog with my wife's new puppy which she's already using with her oncology patients to keep their spirits up while they are getting chemo.
In the field, co-worker didn't use O.P. sack. He hung his food. I didn't hang my food (no bears, but a lot of rodents). My food in plastic bags inside of O.P. Sacks - actually tripled bagged - yeah...i know...perhaps overkill. His tent, pack, and plastic storage bags were all bitten through by a bold nocturnal rodent raider to get to a candy bar - still in wrapper - that he forgot was inside of his pack. My gear and food untouched.
As far as i'm concerned O.P. Saks work.
Note: A friend of mine an ex-USAF and long-time professional dog trainer (IMHO, the best i've ever encountered) has many Shutzhund competition dogs and a large clientelle. He has stated that next to him, i was ("was", not "am" - it was about 20yrs ago he said this) the best dog trainer he knew in the State at that time - he was probably being kind and was exaggerating. I use something akin to the Koehler method which is staunchly based upon an understanding of canine psychology as the proper foundation and basis for all canine training. Just "Google" Bill Koehler is interested - amazing credentials. Most public libraries have one or more of his four books.