Swapping front and back colors with Push-Pull?



I’m accustomed to inside out volumes when I need them, and I can kind of understand SketchUp trying to help me from creating an inside out volume with the push pull tool, especially for beginners. With default colors to start, nothing much surprising happens, but with a pre-existing paint color, why does SU swap the front and back colors on one of the directions?

Default color surface:

Front side already painted. Watch the front an back colors trade places in Entity Info with the red/default surface.

If SU is going to “help” me by turning “front face out” in either case, why can’t it leave the front face color as is and make a red exterior volume either way? It’s tempting to “fix” the colors by selecting all and reversing faces, but that really would make an inside out volume.


I’ve never noticed that before but then I can’t say I’ve ever applied a material to a face before extruding it, either. Is it a bug or a feature?


Yes, if you start modeling with a default painted surface and then paint it afterward, it’s seamless, but if it has a front color to begin with, if feels as if it’s two “helpful” features stacked on top of each other, which is the opposite of being helpful, at least in this case.


And I thought it was just me being stupid… I often assign material to a face before PP’ing the face… and get unexpected front materials inside my volumes… I will take a little more care next time… thx


Is there a benefit of applying materials to 2D faces that you know will become part of a 3D shape anyway? We frequently see problems created by users who apply materials early in the modeling. A common example is reversed faces which are masked by the materials that cause problems in rendering or 3D printing. Another is reduced computer performance because the textures have to be processed by the GPU and we see all too often that users have marginal GPU’s anyway. I teach my students to hold off on applying textures until late in the modeling process.


As has been said in this forum for years • Model FirstPaint Second

Even simple materials (plain color, not texture) can slow frame rate by up to 50%


As I see it this break the principle of least astonishment. Even if it’s been stated in the forums it’s better to model before painting, a user that has never been on the forums should be able to use the program without being confused of what it is doing. Consistency is king for designing a great user experience, and this behavior isn’t consistent.


Maybe this bug-feature is why people are having problems.

That might be true in an ideal world, but reality doesn’t often play out that way. SketchUp first and foremost is pitched and sold as a design tool, and the design process isn’t so linear.

The design process:

  • Doesn’t just go forward - It’s often a “two steps forward and one step back” type of trial and error process.
  • Is classically an iterative loop process - Creation, presentation, critique, and back around the loop again.
  • Creates multiple, parallel choices or options to choose from before moving on
  • Moving on involves multiple steps of increasing detail and refinement - The age old standard process pitched by the AIA calls out Schematic Design (SD), Design Development (DD), and Construction Documents (CD) phases where design starts out crude and simple and gets increasing levels of detail as time goes on. An SD model may be low poly, surface modeled with lots of face me people an trees, but by DD and certainly CD, there are lots more detail, and thickness/solid objects to everything.

All those things mean that in the course of a project there are, say, dozens of times you’ve reached some form of “completion” and presentation of a SketchUp model, only to have to go back and edit it some more.

It was a case of that fourth item, pulling apart a simple design model and trying to model it into more detail, where I stumbled across this discovery in the initial post.

To recap, I see two actions happening here.

  • If SketchUp wants to make it hard (but not impossible) for people to make inside out solids, I can understand that.
  • After that, I don’t see the value in swapping face colors after righting the face orientation.

Unless someone can show me what the value or purpose of that second feature is, I think it should be changed.


One of the problems that I was thinking of when I wrote that is that they end up masking reversed faces which, as has been discussed, ad nauseum, creates issues for some rendering programs as well as 3D printing.


True enough. Perhaps I should say: It’s hard enough to grasp and pay attention to front/back as an issue, so having the program (seemingly at random) swap the paint colors of front and back only adds to the difficulty.

This discussion now has me looking at Monochrome Face style, which I’ve hardly ever used, for speeding up modeling. I would hope it helps with the above issue. Does anyone else like to use this feature?


My default template style includes the Monochrome face style although I don’t really have any trouble leaving the Paint Bucket alone until it’s time for it. :wink: