How to edit a thin wall


I’m a total newbie to making organic models. I have downloaded this: Tiki Mug by Shapespeare - Thingiverse and I’m using an iPad Pro.

I want to smooth the inside and because I want to 3D-print this I’d like to add some thickness just under the eyes.

The smoothing I think works great but when I try to add to the thickness it “goes straight through” the model, I don’t know how to describe it better…

Would really appreciate some tips :slight_smile:

Just as an option:

Export your model as filled and open it with another software to make it hollow. There are apps which can hollow out 3d models.