Every CAD office eventually has the CTB-versus-STB argument, and it usually generates more heat than information. Here's the version without the folklore.
What plot styles actually are
A plot style maps drawing appearance at plot time: line weight, line color, screening (ink density), line end/join styles. The plot style table is the lookup key — and the two formats differ in what they key on.
CTB: color-dependent tables
The key is color index (ACI). Color 1 plots one way, color 2 another — for every object in the drawing sharing that color.
- Line weights live in the CTB file, mapped by color
- 255 slots, one per color
- The discipline: your layer color scheme IS your line weight scheme — red = heavy, cyan = thin, etc.
- The trap: anyone overriding an object's color silently changes its plotted weight
STB: named plot styles
The key is an arbitrary named style attached to objects or layers — "Heavy," "Thin," "Screened-50" — independent of color.
- Line weights live in named styles; colors are free to mean what you want visually
- Color becomes presentation, not plot semantics
- The trap: requires PlotStyle column discipline in layers; mixing eras of defaults gets messy
The real trade-off
CTB wins on: legacy compatibility (decades of drawings and industry convention), simplicity for small teams, the "color equals weight" mental model that older detailers carry in their fingers.
STB wins on: visual freedom while drafting (dark backgrounds want bright colors; plots want black lines at weights), standards that survive layer-color changes, cleaner mapping to modern annotation approaches.
Neither is wrong. The actual failure mode isn't picking the "wrong" one — it's mixing them, because a drawing is bound to one mode at creation (MODELTYPE system variable; the template decides) and converting between them is genuinely painful.
The decision procedure
- Check your ecosystem first. If your clients, consultants, or government deliverable specs mandate one (many DOTs historically specified CTB), that's the decision.
- Check your library. If 20 years of detail library is CTB, the conversion cost decides the argument more than any theoretical merit.
- New office, greenfield? STB's flexibility usually wins today — but only if you also standardize the named style set. An undisciplined STB is worse than a disciplined CTB.
The hygiene that matters more than the choice
- One canonical plot style table per office, version-controlled, referenced in every template
- Named .ctb/.stb files embedded in template setups so drawings travel with their style reference documented
- A "plot preview before PDF" habit — DWG To PDF.pc3 + correct table is the quality benchmark
- Standards written down: which color/style plots at which weight. The folklore exists because this page usually doesn't.
We track CAD tooling standards and keep a free engineering toolbox at CADGuide.tools — no signup, nothing uploads.
Top comments (0)