Why your slicer thinks your filament weighs nothing

This one cost us an afternoon, so it is worth writing down.

A slicer works out how much filament a print uses as a volume, from the toolpath. Turning that into grams needs the density of the material, and turning grams into money needs the price of the spool.

Several slicers ship bundled filament profiles with the density field set to zero. Not missing, not wrong: zero. Anything multiplied by zero is zero, so a part made of a material with no density weighs nothing and costs nothing in plastic.

Why it is easy to miss

Because the rest of the estimate is right. The print time is right, the length of filament is right, the preview is right. The only thing that is wrong is the one number you are quoting from, and it is wrong by all of it rather than by a bit, which is oddly harder to notice.

It also only matters if you quote on material. A shop pricing mostly on machine time barely sees it, which is another reason it survives in a profile for years.

What to do

• Check the density on every filament profile you quote from, not just the ones you set up yourself.
• Use the figure from the spool you bought. PLA is usually around 1.24 g/cm3 and PETG around 1.27, but brands differ and filled filaments differ a lot.
• Sanity-check one print: slice something you have made, compare the predicted mass against the part on your scales.