To hollow an STL file 3D model without supports, use slicer software (e.g., Cura, PrusaSlicer) with built-in hollowing tools that rely on self-supporting infill instead of traditional supports.
These tools let you set a thin outer wall (usually 1-3mm) and fill the interior with lightweight structures like honeycomb or gyroid infill—no extra supports needed. This cuts material use while keeping the model strong.
For beginners, start with 2mm walls and 10% gyroid infill (a balance of easy printing and low collapse risk). Test a small section first to confirm the infill works for your model.