In order to make relative path for Mantaflow Cache in Blender 2.90, please follow the following steps:
Mantaflow is the new physically-based fluid simulation framework in Blender for gas (smoke & fire) and liquid simulations. It completely replaces the existing fluid simulation systems and changes the way you work with fluids.
First method: Select “Relative Path” option in the “Blender File View”
Second method: “File” —> “External Data” —> “Make All Paths Relative”
Please watch video to see how it works:
Hope that our instruction is useful for you to make relative path for Mantaflow Cache in Blender 2.90.
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