How to Use Filled Surface Feature in SOLIDWORKS

The Filled Surface feature creates a surface patch inside a closed boundary. It is useful for repairing openings, closing surface gaps, replacing damaged imported faces, and building smooth patches between existing edges. A filled surface does not have thickness by itself; it creates surface geometry that you can knit, trim, thicken, or use as part of a larger surface model.

When to use Filled Surface

Use Filled Surface when a simple extrude, loft, boundary surface, or planar surface does not give you the patch you need. It works especially well for small openings that are surrounded by existing edges. Common examples include closing a hole in an imported surface body, replacing a missing face, or smoothing the transition between several trimmed surface edges.

If the opening is flat and completely planar, a Planar Surface may be faster. If the shape needs strong control from one direction to another, a Boundary Surface or Lofted Surface may be easier to tune. Filled Surface is best when you have a closed loop and want SOLIDWORKS to solve a patch that blends into surrounding faces.

Prepare the boundary

Filled Surface works best when the boundary is closed and clean. Select edges, sketch entities, or curves that form the opening. Before starting the feature, zoom in around the entire perimeter and look for tiny gaps, duplicated edges, or overlapping sketch segments. Small problems in the boundary are a common reason the filled surface preview fails.

Create the filled surface

1. Open the part that contains the surface opening.
2. Go to Insert > Surface > Fill.
3. Select the boundary edges, sketch lines, or curves around the opening.
4. Choose contact, tangent, or curvature control for the selected edges.
5. Add constraint curves if the patch needs more shape control.
6. Preview the surface and accept the feature when the shape looks correct.

Choose contact, tangent, or curvature

The edge condition controls how the new patch meets the surrounding geometry. Contact is the simplest option; it only connects the patch to the boundary. Tangent makes the filled surface flow in the same direction as adjacent faces. Curvature gives a smoother transition, which can be useful for visible surfaces, molded parts, and consumer-facing shapes.

Do not automatically choose the smoothest option for every edge. Curvature control can make the feature harder to solve if the surrounding faces are not clean or if the opening has an awkward shape. A practical workflow is to begin with contact, confirm the patch builds, then improve selected edges to tangent or curvature where the surface quality matters.

Use constraint curves for shape control

Constraint curves guide the filled surface across the opening. They are helpful when the patch bulges, dips, twists, or ignores the shape you expected. A constraint curve can be a sketch curve, projected curve, or existing model curve that crosses the opening and gives SOLIDWORKS extra information about the intended form.

Use only the constraint curves you need. Too many curves can overconstrain the patch and make it harder to rebuild. For most repairs, one or two carefully placed curves are better than several curves that compete with each other.

What to do after the surface is created

After the filled surface is accepted, inspect it from multiple angles. If it is part of a surface body, you may need to use Knit Surface to join it to the surrounding faces. If the model needs to become solid again, use the knit options or the Thicken feature depending on the condition of the body.

If the patch creates wrinkles or visible ripples, edit the feature and reduce the edge continuity, simplify the boundary, or adjust the constraint curves. Sometimes splitting a complicated opening into two or three smaller filled surfaces gives a cleaner result than forcing one large patch to solve everything.

Troubleshooting failed filled surfaces

If Filled Surface fails, first confirm that the boundary is closed. Next, try using contact on all edges and remove optional constraint curves. If that works, add continuity and guide curves back one at a time. This makes it easier to find the edge or curve causing the failure.

For imported geometry, use repair tools to fix bad edges before creating the patch. For native SOLIDWORKS geometry, look for sketch relations, trimmed surfaces, or tiny leftover faces that make the boundary less clean than it appears. A clean boundary and simple feature setup usually solve most Filled Surface problems.