What Is Transmission Distance (TD) in Filament Painting?
Definition
Transmission distance, or TD, is the thickness of a filament at which it effectively hides the color printed beneath it. Filaments with a low TD, like black, become opaque in a few layers; filaments with a high TD, like many yellows and whites, stay translucent for longer.
Also called: TD, HueForge TD, blending distance.
TD is the single most important number in filament painting. If the TD values in your planning tool do not match your real filament, the print will not match the preview: colors will look muddier or brighter than expected.
Why it matters
A filament painting relies on partial transparency. A high-TD color placed over a darker one needs several layers before it shows its own color; a low-TD color covers almost at once. Swap heights planned without accurate TD values land in the wrong place.
Using TD
Enter each spool's TD in the filament painting planner and watch the preview change. Measure your spools once, keep the numbers with your filament, and your previews will stay honest.
Questions
How do I measure TD?
Print a stepped calibration piece in the filament over a contrasting color and find the step where the color below disappears, or use a dedicated TD meter. Some filament makers publish TD values.
What are typical TD values?
Black PLA is often around 0.5 to 0.8 mm. Many whites sit around 2 to 3 mm, and yellows can be higher. Values vary by brand and batch, which is why measuring beats guessing.