Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
$\begingroup$Your mesh isn't thick enough. Do you have a solidify modifier on there? If you do, up the thickness. Otherwise, you are going to have to grab the faces on one side of the mesh and pull them perpendicular from the mesh to create thickness.$\endgroup$
$\begingroup$Usually it works best to apply subsurf when your model is done. Try hiding subsurf, and adding solidify and see if that works better. Although solidify should be done first. More pictures, details of your model, or a .blend would help others inspect further.$\endgroup$