Fondant vs. Buttercream

Words in italics adapted from The Knot:

Fondant: A sugar dough, made from gelatin, sugar (sometimes also corn syrup), glycerin, and water. It is rolled out into a large sheet and draped over the cake before being smoothed out by hand. While some people don't completely love the taste, it creates a smooth surface for decorating, seals in the moisture of the cake beneath, and can sit out for long periods of time.

Buttercream: A creamy combination of butter and sugar (and sometimes flavorings, such as vanilla extract). Buttercream is soft and is frosted onto the cake using a palette knife. It tastes delicious, but even in the hands of a skilled pastry chef or cake decorator, it can never look as smooth as fondant. Buttercream has a hard time withstanding heat and humidity.

To illustrate, we compare a Sarah Magid cake, frosted entirely in buttercream (with handmade gumpaste flower accents), to a Zoe Clark blossom-applique cake covered in fondant (which was featured on a recent cover of Wedding Cakes: A Design Source).

Admittedly, Sarah Magid is known for texturing her buttercream deliberately, so it looks more natural and immediately edible.  Buttercream, in skilled hands with smoothness as a goal, can be made glassy and sleek.  But I love working with fondant, mostly because it does such a good job of keeping cakes fresh during the many hours (sometimes days) it takes to apply elaborate decorations to them, and also because fondant-covered cakes are better suited to summer weddings (when most everybody chooses to get married). When it's hot enough outside, buttercream can melt into a sloppy mess. That's not to say that fondant is immune to heat/humidity, but it holds up a lot better.  Really, the choice depends on your design aesthetic, and where your cake is going to be displayed. If your reception is formal and you crave the smoothness that screams 'couture cake', fondant is your best bet.  If your reception has a more relaxed tone, and your aesthetic is vintage/rustic/natural, buttercream is probably where you're headed. If your reception is outdoors, and the cake is going to be outside for any length of time (even under cover of shade), fondant is the more prudent choice.  Of course, an air-conditioned hotel ballroom is the perfect habitat for any sort of cake, buttercream included, rendering the temperature outdoors moot.

Ultimately, it's a decision to make in conversation with the person who is going to create your wedding cake. Most bakers and cake designers have their own opinions on the buttercream/fondant 'debate', and you will, no doubt, have your own preferences. Declare them to your baker, but keep an open mind.  

Finally, something to note: what some bakers call buttercream contains no butter at all. There are recipes for 'buttercream' made from solid vegetable shortening and/or margarine, combined with artificial vanilla flavoring and confectioner's sugar. It's usually easy to tell these apart from real buttercream, in that the versions with shortening leave an oily film on the roof of your mouth, while the butter versions melt away completely. The reason for this is that the melting point of butter is 82.4-96.8 °F, which means that in the warmth of your mouth (usually around 98.2 °F), butter releases its flavor rapidly and provides that characteristically silky mouthfeel.  In contrast, Crisco (vegetable shortening) melts between 117°F and 119°F - your mouth is not that warm.