Verify FreeCAD Solid Is Watertight and Manifold

Verifying that a 3D model is watertight and manifold in FreeCAD is essential for successful 3D printing, CNC machining, and finite element analysis. A manifold or watertight model has a continuous, fully enclosed outer boundary with no holes, self-intersecting faces, or stray zero-thickness edges. FreeCAD provides several built-in methods across the Part and Mesh workbenches to test geometry, detect defects, and ensure a model is completely solid.

Method 1: The Part Workbench "Check Geometry" Tool

The most accurate way to verify native parametric shapes (B-Rep solids) is using the Check Geometry tool.

  1. Switch to the Part Workbench using the workbench selector.
  2. Select the final feature or solid object in the Model tree view.
  3. In the top menu, go to Part > Check geometry (or click the magnifying glass icon with a checkmark).
  4. In the Tasks panel on the left, click the Run check button.
  5. Review the results:
    • A completely manifold and watertight model will return "Shape is valid" without error entries.
    • If the model has issues, the report will highlight errors such as Self-intersection, Face non-planar, Degenerate wire, or Non-manifold edge. Clicking on an error highlights the affected geometry directly in the 3D view.

Method 2: Inspecting the Data Properties

You can quickly confirm whether FreeCAD recognizes your design as an enclosed volume through its shape properties.

  1. Select your object in the tree view.
  2. Look at the Property view in the lower-left corner and click the Data tab.
  3. Expand the Shape property.
  4. Verify the ShapeType:
    • It should state Solid or CompSolid.
    • If it states Shell, Face, or Compound, the geometry is open and not watertight.

Method 3: The Mesh Workbench "Evaluate & Repair" Tool

If you plan to export your model to STL or 3MF for 3D printing, evaluating it as a triangle mesh is the most reliable way to check for slicer compatibility.

  1. Convert your solid to a mesh: select the object, switch to the Mesh Design Workbench, and click Meshes > Create mesh from shape....
  2. Select the newly generated mesh object in the tree view.
  3. Go to Meshes > Analyze > Evaluate & Repair mesh....
  4. In the dialog box, review the automated checks:
    • Manifold: Click Check. It must report 0 non-manifold edges.
    • Flipped normals: Click Check. It must report 0 flipped normals.
    • All above tests together: Click Analyze at the bottom to test for non-manifold points, folds, self-intersections, and degenerated faces simultaneously.
  5. If defects are found, use the corresponding Repair buttons within the dialog to automatically fix open seams or flipped triangles.