Marshmallow fondant is a type of fondant made from marshmallows and powdered sugar. It is easily made at home, and many people prefer the taste of this variety compared to other fondants. Similar to other forms of fondant, marshmallow fondant does best when not stored in the fridge. The moisture in a refrigerator can affect the texture of the marshmallow fondant, causing it to soften and melt. Instead, you should wrap the fondant in plastic wrap and store it in an airtight container at room temperature.