SketchUp reversed faces: why they're blue and how to fix them
A blue-grey face in SketchUp is the back of a face pointing outward. Right-click it and choose Reverse Faces, or right-click a face that points the right way and choose Orient Faces to make every connected face match it.
Why are some faces blue or grey?
Every face in SketchUp has two sides. With the default style, the front is white and the back is blue-grey. SketchUp's own advice is to keep the white front facing out and the blue back facing in.
A face drawn flat on the ground shows its back side facing up, and imported geometry and mirrored copies often come in inside out. It isn't damage. The face is fine; it just points the wrong way.
Does it matter?
For a quick sketch, not much. It starts to matter when:
- You render. SketchUp warns that mixed face directions can cause problems in rendering software.
- You 3D print. Face direction tells the slicer which side is inside the part. Reversed faces can confuse it.
- You paint. Paint applied to a face from the back goes on the back side. It looks fine in SketchUp, but the front is still unpainted and the paint sits on the inside of the model.
How to find reversed faces
On an unpainted model, look for blue-grey. Orbit all the way around, including underneath.
On a painted model, paint hides the problem. Switch to View › Face Style › Monochrome so materials are hidden and only the front and back colours show. Switch back to Shaded with Textures when you're done.
If your style's back colour is hard to tell from the front, change it in the Styles panel (Window › Styles on macOS, Window › Default Tray on Windows), on the Edit tab under Face Settings. A strong back colour makes reversed faces easy to spot.
Faces inside groups and components only change while you're editing them. Double-click the group or component to open it first.
How to fix them
One face, or a few that don't touch
- Select the face (or Shift-click several).
- Right-click and choose Reverse Faces.
A whole object that is mostly reversed
- Open the group or component if the faces are inside one.
- Right-click one face that already points the right way.
- Choose Orient Faces. SketchUp turns every connected face to match the one you clicked.
Orient Faces only follows faces that share edges. To reverse single faces on a smoothed surface, turn on View › Hidden Geometry first.
If the face was painted on its back
After you reverse it, the paint is on the inside. Paint the front again with the Paint Bucket.
How Lookover fixes reversed faces
One of Lookover's always-on checks, which run without AI, looks for faces that are unpainted on the front but painted on the back: the case paint hides from you. It reports how many faces are affected and in which objects, and its Fix it button flips those faces and moves the paint to the new front side. It is one undo step.
That check doesn't flag reversed faces with no paint on either side, because those are easy to see as blue-grey. For those, use Orient Faces as above. Lookover also notes mirrored copies, which often show faces inside out.
Questions
What is the difference between Reverse Faces and Orient Faces?
Reverse Faces flips exactly the faces you selected. Orient Faces makes all faces connected to the one you clicked point the same way as it. Use Reverse Faces for a few faces and Orient Faces for a whole object.
Why can't I select or reverse the faces?
They're probably inside a group or component. Double-click it to edit it, then select the faces. If the group is locked, unlock it first from the right-click menu.
Can I change the blue back-face colour?
Yes. Open the Styles panel (Window › Styles on macOS, Window › Default Tray on Windows), go to the Edit tab and choose Face Settings. Front Color and Back Color set the colours for unpainted faces. Paint on a face overrides them.