Slicer modifiers: change infill or settings on just one part of a model

What a modifier actually does

By default, every slicer setting applies to the whole part: the same infill, the same wall count, and the same layer height from the first layer to the last. Real parts rarely need that. A mounting tab takes far more load than a cosmetic shell, and the area around a screw hole needs more plastic than the middle of a big block. Prusa's documentation describes modifiers as a way to change settings for just one section of a model. Its examples are denser infill or extra perimeters for added stiffness.

The payoff is efficiency. Cranking up global infill to beef up one corner burns filament and stretches print time, which is exactly the trade-off Prusa calls out. A modifier puts material only where it does real work. It works in reverse too: you can lighten a region, strip out solid layers, or switch extruders on part of a model. If infill density and patterns are still fuzzy, start with our infill guide.

Three ways to mark the area you want to change

According to the Prusa Knowledge Base, PrusaSlicer gives you three ways to define the affected region. A height range modifier splits the model into horizontal bands, and each band gets its own settings. A primitive modifier mesh is a simple shape that you drop into the part: a box, cylinder, sphere, or slab. A custom modifier mesh is a shape you modeled ahead of time in a 3D program and then load into the slicer.

Pick the tool that matches the shape of the problem. A horizontal band, like the base of a bracket or a section of tube, is a natural fit for a height range. A small, localized spot, such as a screw boss or a hinge knuckle, is easier to cover with a cylinder or a box. An irregular region is worth a custom mesh. Prusa notes that loading a custom shape is only available in Expert mode. The same menu also lets you add text, an SVG, or an item from the program's gallery as a modifier.

Adding a shape modifier, step by step

In PrusaSlicer, right-click the model, choose Add modifier, and pick a shape. It shows up in the 3D view and in the Object list on the right. Use the regular Move, Rotate, and Scale tools until the shape covers the area you care about.

One rule explains how modifiers behave: Prusa's documentation says custom settings apply to the intersection of the modifier mesh and the model. Any part of the shape that sticks out into empty space does nothing. A slightly oversized box is harmless, so placement is more forgiving than it looks. To edit the modifier's settings, right-click it in the 3D view or click the gear icon next to it in the Object list.

Two handy details. If you scale the model, the modifier scales with it and keeps its size and position relative to the part. And if you moved the modifier up off the bed, a button in the Part manipulation panel drops it back down.

Height range modifiers and per-band layer height

Right-click the model and choose Height range modifier. A Height Ranges panel opens at the bottom right. Add or remove intervals there with the plus and minus icons, and each interval then appears in the Object list. Click the gear icon next to an interval to choose its settings. Per Prusa, Normal mode gives you infill plus layers and perimeters. Expert mode adds speed, ironing, fuzzy skin, extrusion width, and advanced options.

Each interval also has its own layer height field. It uses the global value by default, but you can slice a single band at a different layer height, such as the detailed top of a figure, while the rest of the part prints at your usual setting. Prusa does warn that a layer height set for the entire object can conflict with the one set on an interval, so check the sliced preview to confirm which one actually applies. For help picking values, see our layer height guide.

Support enforcers and blockers work the same way

According to the Prusa Knowledge Base, custom supports work the same way. Instead of a modifier, you add a support enforcer to force supports in a spot or a support blocker to keep them out of an area. Supports are generated where the enforcer intersects the main model. Prusa points out that you need to enable support enforcers in the drop-down menu above the model list. Otherwise they have no effect.

This comes in handy when auto-generated supports overshoot, for example inside a narrow hole where they would be impossible to dig out. It also helps when they undershoot, such as under a small overhang the slicer decides is fine. For everything else, from support density to support styles, see our guide to print supports. Modifiers, enforcers, blockers, and height ranges all live in the same right-click menu, so once you learn one, the others come easily.

Real examples and the limits worth knowing

Prusa's own examples show how far the idea stretches. One pairs two modifiers. A box-shaped modifier removes the top and bottom solid layers, and a plane-shaped modifier turns them back on and switches to extruder 2 on a printer fitted with an MMU2S. Another example turns a model downloaded from Thingiverse into a piggy bank. The hollow interior and the coin slot are primitives created in the slicer, with infill, perimeters, and top and bottom layers all set to zero. Prusa's takeaway is that you can do basic remixing without leaving the slicer.

Keep two limits in mind. The more modifiers you stack, the harder it gets to tell which setting applies where, so always step through the sliced preview layer by layer before you hit print. Also, this guide follows PrusaSlicer's documentation. If you use a different slicer, check its docs for what it calls these tools and how it handles them.

Sources and limits

• Prusa Knowledge Base — Modifiers
• Prusa Knowledge Base — Modifier meshes, custom supports and other magic

We organize manufacturer and community documentation; we have not measured these products ourselves. The manual for your exact model takes precedence over general guidance.