What will happen if fondant is heated over 37 Celsius?

If heated above 37 degrees Celsius (98.6 degrees Fahrenheit), the sugar syrup in the fondant will start to melt and the mixture will become soft and runny, losing its stiff consistency. This will make it difficult to work with and may cause the fondant to deform or collapse. To prevent this, it's important to keep fondant at a cool temperature, ideally between 18 and 22 degrees Celsius (65 and 72 degrees Fahrenheit).