Mastering Boundary Fill in Fusion: Blend Surface and Solid Modeling Like a Pro
Updated November 8, 2025
Boundary Fill is a powerful tool in Fusion that bridges surface and solid modeling. If you're looking to create intricate designs with precision and ease, this guide—and the embedded video below—will walk you through the essential steps.
The Flexibility of Surface Modeling
Many users might jump straight to extruding a solid vase from the bottom pattern, but surface modeling offers unmatched flexibility. For intricate shapes, like a vase with a delicate top, surface modeling allows more control and adaptability. This workflow starts with just three simple lines that form three critical surfaces, setting the foundation for the Boundary Fill command.
A surface modeling setup in Autodesk Fusion showing curved and flat surfaces intersecting around a spline sketch. These surface boundaries will later define the closed region used to generate a solid body inside through the Boundary Fill command.
Understanding Boundary Fill
Boundary Fill is designed to fill the space between selected boundaries, converting enclosed volumes into solid bodies. In this case, the vase's closed volume is defined by:
The patterned bottom surface
A curved top surface
A flat bottom surface
Autodesk Fusion Boundary Fill setup showing selected surface bodies highlighted in green. The intersecting curved and flat surfaces define a closed region that will be converted into a solid body using the Boundary Fill tool.
These boundaries intersect to create a "cell," which represents the enclosed volume. Using Boundary Fill, we’ll select this single cell and turn it into a solid body.
Autodesk Fusion Boundary Fill tool creating a new solid body from intersecting surfaces. The selected region in green represents the closed space formed by curved and flat surfaces, which is converted into a solid using the “New Body” operation.
Key Features You Should Know
Operation Types: Decide how the new solid body interacts with existing geometry.
Remove Tools Checkbox: Choose whether the original surfaces should remain visible or be removed after the operation.
Once the operation is complete, the new solid body will appear in your project browser, ready for further adjustments.
After completing the Boundary Fill operation in Autodesk Fusion, the new solid body can be modified using standard solid modeling tools. This image shows the Shell command being applied with a 3 mm wall thickness, demonstrating how easily surface-based designs transition into editable solid models.
Why Use Boundary Fill?
Boundary Fill streamlines the process of blending surfaces and solids, making it perfect for complex shapes and creative designs. After creating the solid, you can leverage Fusion's parametric tools to refine and enhance your model effortlessly.
Watch the Video Tutorial Below
For a detailed walkthrough of this process, check out the embedded video at the bottom of this post. It provides a step-by-step guide to using the Boundary Fill tool effectively, helping you gain a deeper understanding of its capabilities.
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