Hi, Is there a way to select only the newly created vertices that solidify creates when it’s applied?
I tried creating a vertex group with all vertices before applying solidify but when I select them after I applied the modifier the newly created vertices are also added to the group 
A roundabout way would be to add an extra material slot to the object, set its index for both material inputs in the modifier. Then you’ll be able to use Select Linked with Material as delimiter, or just click Select in the material buttons.
That is not perfect but works well enough. Thanks!