I see them used for 3d bear pans . Never made one myself, but want to know when and why I would use one. I'm trying all things new to me to get experience and see what all I can do. I really love to bake and decorate. You guys seem so knowledgeable and seem to be very quick on the good advice. Thanks in advance for replys! 
the heating core is used when either:
a. you have a cake that domes up in the middle... it promotes more even baking and decreases the hump (thereby reducing the amount you shave off when levelling). for this, you don't really need a "heating core", you can use a flower nail, turned upside down and greased in the middle of your cake pan.
b. you have a cake that is going to bake faster on the outside (so it'll get crusty or burnt) and remain liquid on the inside (i.e. 3D bear pan). it allows the inside to bake at a similar rate to the outside.
HTH
The only d pan I have is the bear pan. No the hole is right up the center and the duck pan does not have one. The barbie doll cake pan has a small tube. As far the whole you can fill iit with buttercream or just leave empty which is what I do. What pan are you asking about??
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