Design AtlasAn injection mold is two halves — core and cavity — that wrap around a part, then separate to release it. If the walls are perfectly vertical (0° draft), the part's surface and the mold wall are pressed together almost like a vacuum seal, so releasing it scrapes the surface or, worse, the part hangs up and tears, or the tool gets damaged. In practice, vertical walls get a small deliberate taper — usually 1–3° — designed in from the start: the wall widens ever so slightly going up, so the moment the mold opens, the wall face pulls itself away from the part surface.
The reason draft matters is friction, not adhesion. The smoother the surface and the deeper the wall, the more draft angle is needed — a textured wall (say, a leather-grain finish) catches on its own texture more easily and needs even more draft. That's why CAD "draft analysis" tools paint a model's faces red (not enough draft) or green (safe), flagging surfaces at risk of not releasing before a mold is ever cut.
A designer who doesn't know this concept renders a perfectly vertical, minimal-looking form, then gets tooling feedback later that the walls need draft and the form has to change slightly. It's worth sketching injection-molded shapes with a barely-visible taper from the very first pass, instead of true verticals.
When to use
When designing vertical walls for an injection-molded or die-cast part — check especially on deep cavities or textured surfaces.