I recently looked into this, and bought some foil barrier bags on Ebay. From my recent reading, my understanding is that barrier bags (designed to prevent ingress or egress of odor molecules, oxygen, and water vapor) are engineered in several different forms. From highest barrier (most odorproof) to lowest, I think they go in this order:
1. Aluminum foil bags
2. Metallized multilayer film bags
3. Multilayer film bags
4. Monolayer film bags
The film material and thickness also makes a difference, obviously. A bag that is twice as thick as another is much more than twice as impervious to odor penetration. Depending on the material, a doubling of film thickness can increase barrier performance tenfold or more. My understanding is that Opsaks are monolayer polyethylene film, like a very thick common ziplock. It is no surprise to me that they failed the test described in that BPL article (with the dogs in the locker room). It doesn't make sense to use a monolayer polyethylene bag to seal in food odors. The NyloBarrier bags sold for the same purpose by Litetrail.com are also probably worthless, in my opinion. They are a monolayer nylon film and they have no seal. Rolling the top of a "hard" film like nylon does not produce a seal.
Aluminum foil bags (aluminum foil laminated to heat-sealable plastic film) are several (or many) orders of magnitude more resistant to odor, oxygen, and water vapor penetration than a monolayer bag like an Opsak or NyloBarrier bag. I bought these:
It says "mylar" in the title but the description makes it clear that it is a foil laminate, not metallized film. I prefer the stand-up pouch style bags to the flat style.