Why the Blender mesh only see half of it?

Questions & Answers
1

Hi, I made a cup mesh in Blender and export it. The first time I lost some faces when I put it into Unity, and I fix it with pressing Ctrl + N to calculate normals. But the second time the mesh didn’t lost faces, it lost half of the mesh. I can see the whole mesh on the top, but it will transparent on the side I view. Why? Please help me, thanks a lot!!!

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Thanks for save and iantlloyd’s answer! But it still didn’t work. When I flip normals, it still show half of it… but show another side. (See the below picture 2) How come?
!

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2

It sure looks like the normals of the outside of the cup is reversed (pointing inwards). You can fix this by selecting the wrong aligned normals and reverse them in blender.

3

if ur using a current version, select backward faces, flip normals with, SPACE > search “Flip Normals”

4

if its your normals theres a way you can view all of your normals to tell which way they are facing and then you can turn them to have the arrows facing up.