How to maintain hollowness when constructing from a hollow mesh？

[kietsuc]

I created a hollow model by using a mesh as the inner structure and performing a Boolean subtraction with an outer mesh. This results in a dual-layer mesh, where one layer represents the outer surface and the other represents the inner wall. After voxelizing the model, I lost the internal structure when converting back from voxels to a mesh. How can I ensure the hollow structure is maintained during this conversion process?