Shell spacing refers to the amount of space between UV shells (also known as shell padding). There are a few things to note when it comes to shell spacing:Texture bleeding: Texture bleeding is when the color information inside one UV shell bleeds into another UV shell due to texture filtering. In general, it's good practice to keep at least 2 pixels around all UV shells so that there is a 2px margin to the texture map border, and a 4px margin between UV shells. However, that only applies to the final version of the texture. If the texture map is further reduced in size by the engine you need to increase this padding.If LOD models are being used, then every LOD/Mipmap step requires double the shell spacing. For example: If you have an asset with 3x LOD steps and an original texture size of 2048px, then on the smallest mipmap level the texture is only 512px. In this case, the spacing needs to be 4px between shells at 512px, then 8px at 1024px, then 16px at 2048px. Thus, when doing the layout you need to make sure that you have at least 16px distance between shells and 8px distance to the UV map border. You can use the UV Toolkit's Measure tool to keep track of pixel distances.