How to Hollow Meshes for Resin 3D Printing in Blender

Hollowing out solid 3D models before resin printing reduces resin consumption, decreases print weight, and minimizes peeling forces during the printing process. While dedicated slicers offer built-in hollowing tools, using Blender provides granular control over wall thickness, interior topology, and the precise placement of drainage holes. This guide covers the complete workflow for creating a hollow mesh with uniform walls and functional drainage channels using Blender's native modifiers.

Step 1: Prepare and Clean the Mesh

Before applying modifiers, ensure the model is manifold (watertight) and has uniform scale values:

  1. Select your object in Object Mode.
  2. Press Ctrl + A and select All Transforms to reset scale to 1.0. Incorrect scale causes uneven wall thickness.
  3. Switch to Edit Mode (Tab), press A to select all geometry, and press Shift + N to recalculate outside normals.

Step 2: Apply the Solidify Modifier

The Solidify modifier creates the internal cavity by generating an offset surface inside the mesh.

  1. Go to the Modifier Properties tab (wrench icon) on the right sidebar.
  2. Click Add Modifier > Generate > Solidify.
  3. Set the parameters:
    • Mode: Change from Simple to Complex for organic or highly detailed sculpts to avoid self-intersecting geometry.
    • Thickness: Enter a negative value matching your target wall thickness (typically between -2.0 mm and -3.0 mm for standard miniatures and figures).
    • Offset: Set to -1.0000 to ensure the walls grow inward without altering the exterior dimensions.
    • Boundary: Set to Round or Flat depending on your model geometry.
  4. Check the box for Even Thickness to prevent thin spots at sharp angles.
  5. In the modifier dropdown menu, click Apply.

Step 3: Inspect the Internal Geometry

Verify that the hollow interior did not create overlapping or inverted faces:

  1. Press Alt + Z to toggle X-Ray Mode, or switch to Wireframe View (Shift + Z).
  2. Look for any internal floating islands or self-intersecting geometry.
  3. If loose geometry exists, enter Edit Mode, deselect everything, hover over the unwanted interior shells, and press L to select linked geometry, then press Delete > Vertices.

Step 4: Create Drainage and Suction Relief Holes

Hollow resin prints require at least two holes: one for uncured resin to drain out, and another to allow air inside to prevent suction cup failures that cause layer separation.

  1. In Object Mode, press Shift + A > Mesh > Cylinder.
  2. Set the cylinder diameter to your desired hole size (typically 2.0 mm to 4.0 mm).
  3. Rotate and position the cylinder so it passes completely through the outer wall into the internal hollow cavity, preferably in an inconspicuous area (such as the base, joints, or undercuts).
  4. Duplicate the cylinder (Shift + D) and place a second one at an opposite end to create an air relief path.
  5. Select the main model, go to Modifier Properties, and add a Boolean Modifier.
  6. Set the operation to Difference, set the Solver to Exact (or Fast if geometry is dense), and select the cylinder as the Object.
  7. Apply the modifier and delete the cylinder. Repeat for the second drainage cylinder.

Step 5: Final Export

  1. Select the finalized hollow mesh.
  2. Go to File > Export > Stl (.stl) or Wavefront (.obj).
  3. In the export settings panel, check Selection Only and ensure the scale is set to 1.0.
  4. Import the file into your preferred resin slicer to add supports and verify the hollow cavity slice-by-slice.