Horticultural charcoal is a substrate material that is essential in keeping your terrarium odor free and it also reduces moisture. You can also use it in your potting soil mix to reduce moisture for your houseplants. You will receive one 3 inch by 5 inch bag of charcoal that weighs about 2 oz. This is enough charcoal for 2 small to medium terrariums or one large one. This item ships first class mail. I am happy to help you create a one of a kind terrarium kit so convo me with any questions or requests.