All plastic breaths a small amount. If you want the best, use mylar bags which cut this air transfer down to almost nothing. These 4 mil thick bags have an outer layer of aluminum and 3 different plastic layers on the inside designed for a wide range of products including long term food storage. For all practical purposes they are light proof, air proof and water proof.
These bags are strong enough to hold a partial vacuum, the main reason, in my opinion, you need them if you are going to use oxygen absorbers and plastic buckets. This is because as the oxygen absorbers absorb the oxygen in the container they don't put anything back in, but rather create a partial vacuum. If you didn't use the bag, your bucket would collapse instead of the bag. The buckets just aren't strong enough to hold this vacuum without being seriously deformed. But the mylar bags can, even though they are thin. For those wanting the very best, these bags will protect your food inside the bucket even if for some reason the lid on the bucket didn't make an airtight seal which seldom happens.
Several people have ask me if they can store food in these bags without putting them in a protective bucket. The answer is no. And that's because they are not in the least puncture resistant. They really need that bucket for support. The bags we sell fit a 6 gallon plastic bucket perfectly. Before you start your operation, you may wish to cut a bag into strips beforehand to test making a few seams in order to get the temperature set correctly on your iron. You want to get the temperature of the iron set so after the bag is ironed closed you can't pull the bag open without destroying the bag. It is also easy to get the temperature set too high which destroys the strength of the bag. It is also possible to set the iron temperature too cool, where the bag looks like it is sealed but the seam can still be pulled apart fairly easily. With our clothes iron at home, the wool setting works just great. But as not all irons are the same, you ought to make a test strip or two to be sure. Even though I have not tried the Eurosealer myself, I've been told it also works great in sealing these bags. To seal the bag shut, place a planed or smooth board across the opening of the bucket, lay the bag across it, and iron the bag shut.