Slicing in 3D printing is the process of converting a 3D model into a set of layer-by-layer instructions that a printer can follow. The software literally slices your digital model into hundreds or thousands of thin horizontal layers, then calculates exactly how the printer’s nozzle (or light source) should move to build each one. The output is a file your printer reads to know where to go, how fast to move, how much material to push out, and what temperatures to use.
How Slicing Works
You start with a 3D model, typically an STL or OBJ file exported from design software. This file describes the shape’s geometry but contains zero information about how to actually manufacture it. The slicer bridges that gap. It takes the solid shape, divides it into flat cross-sections at whatever layer height you choose, and then plots a toolpath for each layer: the exact route the print head follows to deposit material in the right places.
The final output for most desktop printers is a file written in G-code, a programming language made up of simple commands. Each command tells the printer one specific thing. Some commands set the nozzle temperature to, say, 190°C. Others move the print head to precise X, Y, and Z coordinates at a defined speed. One key command (G1) handles linear movement and can simultaneously push a specific length of filament into the nozzle while the head travels. Together, thousands of these commands executed in sequence produce a physical object.
Slicing for Filament vs. Resin Printers
Filament (FDM) printers and resin (SLA) printers both require slicing, but the output looks different. For FDM, the slicer generates toolpaths: precise routes the nozzle follows while extruding melted plastic, layer after layer. For resin printers, the slicer produces image masks instead. Each layer becomes a 2D image that a light source (laser, projector, or LED array behind an LCD screen) projects onto liquid resin, curing it into a solid shape one slice at a time. The concept is identical, but the instructions change to match the hardware.
Layer Height and Print Quality
Layer height is the single biggest factor affecting quality, speed, and strength. It determines how thick each horizontal slice is. A common starting point for FDM printers with a standard 0.4 mm nozzle is 0.2 mm, which is 50% of the nozzle width. If you want faster prints and can accept slightly rougher surfaces, you can go up to about 0.32 mm (75% of nozzle width). For finer detail, you drop lower.
Resin printers push this further. Some support layer heights as thin as 25 microns (0.025 mm), producing extremely smooth surfaces where individual layers are nearly invisible. The tradeoff is time: printing at 25 microns instead of 100 microns roughly quadruples print duration because the printer must complete four times as many layers. Unless you need the extra resolution for fine details, thicker layers are generally the better choice.
Infill Density and Patterns
Most 3D-printed parts aren’t solid inside. The slicer fills the interior with a partially hollow structure called infill, saving material and time while still providing strength. You control two things: the density (how much of the interior is filled) and the pattern (the shape of that fill).
Density is expressed as a percentage. Decorative parts that won’t bear any load do fine at 5 to 10%. Parts for typical use land in the 10 to 20% range. Load-bearing or structural pieces need 40 to 60%, and parts that must survive impacts may go up to 80 or 90%. Interestingly, 100% infill can actually be weaker than 90% because there’s no room for the printer to compensate for slight overextrusion, leading to internal pressure and defects.
Pattern choice depends on where stress comes from. Grid (a simple crisscross) prints quickly and handles single-direction loads well. Gyroid, a complex wavy lattice with no straight lines, provides uniform strength in all directions and prints surprisingly fast. Honeycomb is material-efficient and strong. Triangular patterns perform well in tensile strength but use more material and print slower. For parts that experience forces from multiple directions, three-dimensional patterns like gyroid or cubic are the strongest options.
Walls and Structural Strength
Walls (also called perimeters or shells) are the solid outer layers of your print. With a 0.4 mm nozzle and three wall perimeters, you get a solid outer shell that’s 1.2 mm thick. Research on the mechanical effects of wall count shows that adding perimeters has a bigger impact on part stiffness per increment than increasing infill density. This happens because perimeter layers fuse along their tops, bottoms, and sides, creating better bonding than infill, which mostly connects only at the upper and lower layers.
For strong prints, 3 to 5 walls is a reliable range. Decorative pieces can get away with 2. If you need to strengthen a part and don’t want to increase print time dramatically, adding one more wall often does more than bumping infill by 10 or 20 percentage points.
Support Structures and Overhangs
Since FDM printing deposits material layer by layer, each new layer needs something underneath to rest on. When part of your model extends outward with nothing below it (an overhang), the slicer can generate temporary support structures to hold that section up during printing. You remove these supports after the print finishes.
Slicers use an angle threshold to decide where supports are needed. In Cura and PrusaSlicer, the default is 45° measured from vertical. Any surface that leans beyond that angle gets flagged for support. You can adjust this threshold if your printer handles overhangs well or if you want to minimize support material. Most slicers will automatically place supports when you enable the option, though you can also add or remove them manually in the preview.
Bed Adhesion Options
The slicer also controls how your print attaches to the build plate during that critical first layer. Three common options exist, each serving a different purpose.
- Skirt: A disconnected outline printed around (but not touching) the base of your part. It doesn’t improve adhesion at all. Its real job is to prime the nozzle and let you visually confirm that filament is flowing correctly and the bed is level before the actual print begins.
- Brim: A single-layer extension that radiates outward from the base of your part, like the brim of a hat. Because it’s physically connected to the print, it increases the contact area with the build plate, reducing warping and improving stability. It peels off easily after printing.
- Raft: A multi-layered grid printed underneath the entire part, acting as a thick foundation. Rafts provide the strongest adhesion and are useful when printing with materials prone to warping, but they consume significantly more material than brims and can leave a rougher bottom surface on your part.
Popular Slicing Software
Cura is the most widely used free slicer as of 2025, largely because it’s open-source and compatible with a huge range of printers. It lets beginners hide advanced settings while giving experienced users access to hundreds of parameters. PrusaSlicer is another open-source option that works especially well with Prusa printers but supports other brands too, and it tends to surface advanced features more readily. Bambu Studio is optimized for Bambu Lab printers. For resin printing, dedicated slicers like Lychee and ChiTuBox handle the image-mask workflow those machines require.
Most slicers include a preview mode that lets you step through the print layer by layer before sending it to the printer. This is worth using every time. You can spot problems like missing supports, thin walls, or unexpected gaps before wasting an hour of print time and a spool of filament.