Urea combines very well in creams that contains Calendula and Shea Butter for cracked heels on the feet.
Be aware that this product can make emulsions thin slightly, so you may need to formulate a thicker texture to start with, using a strong emulsifier.
According to the Cosmetic Ingredient Database (Cosing), the functions of Urea are:
Antistatic, Buffering, Humectant, Skin Conditioning
To view more information, visit the Cosing Database here