I’m working on a Project that Prominently Features a Red PETG Top Surface that after the Printing is done gets Sanded with Grits from 400-2000 +Heat Treatment.

There is a Big Issue tho, After the Sanding is done, I can Rather Prominently see the Walls and Infill of the Layers Below. At first I suspected that I just sanded too much and that the internals weren’t really filled in 100% as they should, but after some testing and Closer Inspection, it just seems the Red PETG is just Transparent enough that I can see the layer below…

So how do I stop this from Happening? Thus Far I played around with Fan Speeds, Nozzle Temps (±10°C), Layer Hight and Ironing all Solid Layers with Mixed Success, non Satisfactory enough however…

  • To continue using the filament you have, you’ll need more top layers as suggested already. The other alternative is to buy a different brand of red PETG with lower light transmission.

    I mostly print in PLA, but there are some brands that are almost translucent while others are opaque after a 0.2mm layer or two and this is all just basic color PLA not anything fancy like silk or the like.

    Also you might try lowering the infill. 100% is typically pretty excessive for strength purposes (60-70% is enough) and ironing the top surfaces might help reduce the amount of sanding needed.

  • I would try adding more top layer shells. That way there’s more plastic between the surface and the first infill layers.

      • Infill is different from top layer shells. The infill is a different pattern from the top and bottom layers, and a different pattern from the walls.

        Usually the top/bottom shells are set to 5 by default, and the walls are 2. If you bump the top and bottom layers to something like 10 or 15, they’ll be much thicker before it switches to the infill pattern.

  • Any filament will have some non-zero transparency when laid in a thin layer. Additionally the bridging across infill will add some surface distortion that can also be visible.

    Is this a multicolor print with a filament swap?

    Add more 3-5 more top layers of red petg to make it more opaque. It may also help to use a different infill style, like lightning, or increase density/add multi-line.

    • The Infill is 100% for the entire Object. Yeah it is a Multifilament system swapping once between black and red PETG