There are many factors that contribute to a cookie's fluffiness, including the type of flour used, the amount of leavening agents (such as baking powder or soda), the ratio of wet to dry ingredients, and even the addition of extra ingredients like marshmallows or cream cheese. All of these things work together to create a soft, fluffy cookie that melts in your mouth. So next time you're craving something sweet, be sure to try a fluffy cookie recipe!