Yes, they are proportional because if you increase or decrease either amount they will both change. They will always have the same size. For example if I want to double the flour, I will have to double the milk as well because they have the same ratio.
The amount of flour and the amount of milk are in direct proportion because when the amount of flour increases, the amount of milk increases. If I want to make a product (e.g. cake) that was 16 times bigger, I'd make the flour 16 times bigger and the milk 16 times bigger.
