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.