It looks like you're using Internet Explorer 11 or older. This website works best with modern browsers such as the latest versions of Chrome, Firefox, Safari, and Edge. If you continue with this browser, you may see unexpected results.
Often, the cause of an unprintable 3D model is the surface thickness. If the surface is too thick, the model can break or crack from internal stress. If its too thin, the model will be extremely fragile.
DON'T ignore material guidelines
Each printing material has its own unique properties with varying flexibilities, smoothness, weight, and so on. Take this into consideration while designing and printing.
DO design large flat sides
Large and flat sides are easier for the printer and have better chances of success than curved or hanging edges.
DON'T design the object with small or curved sides
This will reduce the stability of the bottom later if a project is too thin or has too many curves.
DO follow software guidelines
Every software package for 3D modeling has at least a small difference among them. Follow the printer's specific software guidelines to get the best results.
DON'T forget to check the resolution
For a file to print correctly, the file needs to have a high-quality resolution for the best results.