This post will give a quick instruction on how you can add thickness to your 3D file by using Blender.
If you don't already have Blender, you can download it HERE.
Step 1. Import your STL file
File -> Import -> Stl (.stl)
Step 2. Click on Modifiers -> Add Modifier -> Solidify
Step 3. Experiment with the settings in order to obtain a satisfactory thickness. For this model, I changed the Thickness to 2.0, Offset to 0, and checked that I wanted 'High Quality No' thus obtaining:
By adding thickness to certain models, it will make thin objects less brittle during a print, thus increasing the probability of achieving a successful print. :)