When storing opened baby formula powder the baby powder formula should be kept sealed with the lid and stored in a cool dry place.
keep the baby formula out of the humidity and have it in a cool place such as in the pantry or cupboard.
You could also refrigerate the powder formula but it's best to just leave the opened baby powder formula covered and sealed and in the pantry, on the counter etc.
If the opened formula is liquid formula then you must always keep it in the refrigerator.
Also if you make bottles of formula then keep them in the refrigerator until ready to feed the baby.
Never leave a bottle of formula out at room temperature longer than an hour because it can go bad and make the baby sick.
I've always just kept the powdered baby formula covered with the lid when not in use and stored it in my pantry.