These are super tough, 6 mil, food grade Mylar foil bags. They hold up to 1.5 gallon, but work best (stack flattest) if they are used for about 1 gallon.
They are shaped so that when filled they take on more of a round flat pillow shape and stack in layers into a 5 or 6 gallon bucket. 4-5 per 5 gallon bucket seems to work best.
Why use these instead of one larger bag? Well....
#1: You don't have to open a huge 5 gallon size bag of one product and risk it going bad or getting bugs before you use all of it. Even if you wish to put up 50 lbs. of one item like rice for example, you are still much better off having 5, 10 lb individually sealed bags in the bucket than you are to have one huge 50lb bag.
#2: The seal on a Mylar bag is an easy place for the integrity of the bag to be compromised. When you heat seal the top of a 20” bag, that is a long seal and you must have a smooth, wrinkle free seal the entire width of the bag. With these bucket bags however, all you have to seal is the end of a 5” wide opening. No more fighting with the sealing iron trying to keep everything lined up and smooth and then worrying about if it is good enough or not.
To use these just fill the bag from the open end “spout”, (You may find it helpful to use a large funnel to fill the bag) drop in an oxygen absorber, then heat seal the opening shut. Now layer the bags inside of your buckets until the bucket is full and put a lid on it.
Think of how nice it would be to have buckets that each have say 10 lbs. of oatmeal, 10 lbs. of white rice, 10 lbs of wheat and so on vs. huge buckets full of one product. It just makes sense.