https://theslyd.tumblr.com/post/161020478636/tutorial-normal-bump-map-baking-in-blender

Long post alert.

Normal mapping, or Dot3 bump mapping, is a technique used for faking the lighting of bumps and dents – an implementation of bump mapping. It is used to add details without using more polygons. - Wikipedia

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For the Sims 4, normal map is best for details like fabric creases. Here’s an example showing the same mesh and texture with/without a normal map. I’m using a solid color as texture map so you can see the bumps clearer.

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“Why not draw the details on the texture map”, you may ask. Because details generated from a normal map behave like real bumps and react to the light, which feels more realistic. While the texture map by itself doesn’t react to the light and looks flat. The difference is quite obvious from this in-game screenshot below.

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Step-by-step guide after the cut.

NOTE: This method requires a high-poly mesh and a low-poly mesh. It won’t work if you only have one mesh.

1-2-3. Prepare a high-poly mesh.

If you’re using Marvelous Designer, which I recommend for this particular tutorial, select the whole mesh and decrease the Particle Distance. I usually set it to 5-10. Change the mesh from triangle to quad, and export to .obj after simulation.

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If you’re editing an EA mesh or modeling from scratch in blender, you can apply a Subdivision Surface modifier and use the Sculpt tool to add some bumps and dents. However, this requires much more work than modeling in Marvelous Designer. I used this method on the Fenty bow slides.

  1. Prepare a low-poly mesh. Follow this tutorial to remesh the high-poly mesh in Zbrush. Don’t be afraid to lose the details you just created while reducing polycount. You’ll get them back in the end.

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  1. Import both high-poly and low-poly to blender. Polish the low-poly mesh. Merge vertices to remove seams, delete unnecessary vertices, add extra vertices/edges/faces, etc.

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NOTE: For texture baking to work, it’s important to ensure both high and low resolution meshes are correctly prepared beforehand. In essence both meshes need to be; 1) co-located, i.e. both in the same place; 2) have their respective Origin points similarly co-located; 3) their respective “Scale:” and “Dimensions:” data set; and 4) be (approximately) the same size. - Source