What Is Infill? What Does It Do?

Infill example
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With additive manufacturing, we can precisely control two aspects of any part: the perimeter (walls) and the infill (insides).

Contrary to popular belief, 3D printed models are rarely ever hollow. Most have at least a basic infill either to improve the physical characteristics of the part or where necessary to reduce the possibility of collapse on the print bed.

What is infill? 

Infill is the structure of the material inside a 3D printed part. Just as the underside of a bridge has interconnecting steelwork, 3D printed parts have an infill that manipulates the part’s physical properties, including strength, structure, and weight.

Infill explainer
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In fact, apart from material selection, nothing else play as big a role in part strength, structure, and weight as infill. Infill is necessary in most cases, and the structure of the infill is highly configurable to meet different design specifications.

Infill density and infill pattern

The two most important aspects of infill are infill density and infill pattern.

Infill density

The infill density is the amount of material used for the infill. The denser the infill, the fuller, heavier and (in theory) the stronger the part. Besides weight and strength, buoyancy and material consumption are also affected by density.

Infill density is measured as a percentage: 0% is hollow, and 100% is solid. Most designers stick to 5% leaps. Standard prints range from 15-50% infill, while functional prints (such as engineering parts) have a 50-100% infill.

Figurines have a lower infill of up to 15%. For flexible parts, the infill provides rigidity, with flexibility determined by the material.

The amount of infill you need depends on what object you are creating.

Infill pattern

The infill pattern is the structure of the infill. These range from basic lines to intricate honeycombs and lattices. Different infill patterns have different characteristics, like higher strength, rigidity, flexibility, buoyancy and weight load.

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Here’s a list of the most common infill patterns:

  • Lines – printed in one direction for strength in two dimensions
  • Honeycombs – provides moderate strength defined by honeycomb density
  • Grids – doubles up the strength and stiffness of lines with weight gain
  • Triangles – strength in two dimensions in the XY plane
  • Cubic – stacked cubes tilted at 45 degrees for strength in three dimensions

Is 3D printing infill necessary?

Infill is necessary to print structurally sound parts.

Sometimes, infill is also necessary to print three-dimensional models in the first place. When printing complex shapes with overhangs and unique geometries, infill provides support and connects print areas. Thankfully, infill is invisible unless exposed.

However, you can also print without infill and with reduced infill. Printing without infill is only suitable for simple shapes but saves material and reduces print time considerably. The same goes for reducing infill percentage.

Infill is a part of 3D printing for standard and functional parts, especially for fused filament fabrication 3D printers. FFF/FDM 3D printers rely on infill, but you can play with percentages to balance time, cost and physical properties.