3D Printing Infill Density and Pattern Affect Strength, Material Use and Print Time, Engadget Says

In FDM or FFF printing, the interior of a model is normally not solid plastic. The slicer creates a web that supports the layers above it and adds rigidity without consuming a full spool of filament. The process is not universal. Resin printers tend to produce solid models unless the file is intentionally hollowed out, Engadget said. For the filament printers most beginners use, infill is one of the settings that can subtly alter the outcome.

Infill density is expressed as a percentage. A model printed at 0 percent is hollow, and higher percentages produce a denser internal structure. A slicer can attempt 100 percent infill, but Engadget said that is rarely necessary. Prusa recommends 10 to 15 percent for most models, while Flashforge recommends 20 percent as a starting point for general use. Neither source treats those numbers as a universal rule, so a decorative figure or test print may need minimal infill, while a bracket that carries weight or takes repeated hits may deserve more internal support.

A hollow print can still work. Engadget reported that a model with a closed bottom and an interior that gradually closes toward the top can print flawlessly at 0 percent infill. A wide flat surface is different because the printer may have to lay filament across a large open area. Without structure underneath, melted plastic from the nozzle can sag. That is why checking the slicer's layer preview before a long print can prevent a problem from appearing hours later.

Increasing infill also increases filament use, weight and printing time. It can improve compression resistance, but the infill percentage is not a complete strength indicator. Wall thickness, print orientation and material choice all affect the final part. Prusa noted that adding more perimeters can be more effective than adding infill when the goal is a stronger part, according to Engadget.

The pattern of the infill matters as well, because the plastic takes the shape of the selected pattern. Slicers offer several options because no single pattern is ideal for every situation. Grid is a simple general-purpose choice. Cubic creates a three-dimensional internal structure that can withstand forces from multiple directions. Gyroid uses continuous curves instead of straight lines and is often used for functional parts that benefit from more even strength in several directions. Lightning infill works differently, branching mainly where upper surfaces need support rather than forming a regular structure throughout the model. It can reduce filament use and print time, but it does not provide the same internal reinforcement as patterns designed for strength.

Engadget said beginners do not need to learn every infill option before printing. A default pattern and a moderate density are reasonable starting points, and they can be replaced when an object provides a reason to do so. A display model, an electronics enclosure and a load-bearing bracket have different functions, so using the same infill for all three does not make sense. For normal models, Prusa says infill over 30 percent is hardly ever needed.