8 inch by 12 inch mylar bags hold approximately 1/2 gallons of freeze dried food. These are perfect for transferring 1/2 gallon mason jar contents into. We store up our freeze dried goods in the mason jars until we are ready load 10 of these.
Harvest Right recommends 7 mil thick mylar and many freeze dryer owners agree. Bags that are less thick may allow dried foods to poke through and break the seal. You may also consider using a vacuum bag inside the mylar for extra protection.