Core diameter is the width of the colored material inside a colored pencil, usually measured in millimeters.
In the Lab, we don't measure core diameter because manufacturers already provide this information.
We're not the diameter police.
We're interested in how pencils actually perform, not how much material surrounds the working point.
Although manufacturers often boast about core diameter, it has almost NO influence on coloring performance.
Unless you're coloring way down on the side of the pencil and using the full length of the exposed core, most coloring takes place within the tiny 1–2mm area at the pencil's sharpened tip.
Read that again: we only use the center millimeters of any core.
The rest of the core is only there for structural support. Most of the core ends up in the shavings bin of your sharpener. It’s pure waste!
A wider core does not better quality or better performance.
And I often suspect wide cores are simply a way to make a fatter pencil without increasing the manufacturer’s wood budget.