UV mesh is distorted, not a reliable representation of the model? Im working on a face model, trying to create a single 2d printable image of the face's texture.
I created the desireable uv layout, used the texture paint tool- stencil brush in order to create the texture. 
Now, after printing the result, I realised that the UV layout that the Blender created does not represent the model in the correct way. I know that after realising that the both parts of the same seams are significantly not in the same size, although these lines are the line in the 3D model.
I realised that there are two kinds of UV unwrapping methods, but I couldn't find any information on the subject, not in stackexchage and not on different manuals on the net.
What is the cause of this distortion? Can the UV unwrap setting fix it?
Thank you in advance
Look at the paper model export add-on, it seems to be exactly what you're looking for.