Mass gainers are for those who are looking to bulk up or gain more muscle mass. These products contain a lot of calories that mainly come from high quality, quickly digesting carbohydrates and lots of protein. Some might have creatine and other amino acids added in the product to further ensure the growth of the muscles.
Since mass gainers contain quick digesting carbohydrates, they are great as a recovery drink or when fueling up before training. To make your very own mass gainer, combine quick carbohydrates such as maltodextrin or glucosepolymers with your desired protein powder.