What filler to choose - Hi my question is, what's the difference between Restylane and Restylane Silk?

They are both Hyaluronic Acid Fillers but, Restylane Silk is slightly thinner than Restylane. This is why Restylane Silk is preferred in the under-eye area. Depending on the volume deficit, Restylane might be indicated as well.  
 

Hello,Good question.  Most injectors that perform "tear trough" treatments (under the eyes) prefer Restylane as this is a smooth gel that is safe, predictable, and offers a solid duration of 9 to 12 months or longer in this area.  Although not FDA approved for tear troughs, this is the most common filler used for this service.  Restylane SILK is a much thinner product which is ideal for fine lines or treatment of the mouth/lips.  It's not clear why your injector would prefer SILK given that Restylane is the better choice as well as a lower price tag.  

Hello, 

Thank you for your question. Restylane Silk is made with a smaller molecule, it tends to look better under the eyes because its softer than the regular Restylane. However both can be used under the eyes. Good luck!