Infill in 3D Printing: Definition, Main Parts, and Different Types

3D printing infill refers to the internal structure of a 3D printed part. This internal structure can be produced using many different shapes. The purpose of infill is to optimize part weight, strength, and printing time. Many different infill patterns exist. These standard designs can be selected in the 3D slicing software menu used to prepare parts for printing.

This article will define 3D printing infill, discuss how to select the correct infill pattern and density, and describe the various infill patterns. 

2. Gyroid: The gyroid 3D printing infill pattern creates alternating wavy lines or curves. This infill pattern takes longer to print than the others. However, the unique gyroid internal structure allows for almost isotropic mechanical properties. Prints are still weaker on the z-axis but this pattern improves the x and y-axis shear strength. The gyroid pattern works well with flexible materials. Figure 3 is an example of a gyroid infill pattern:

3. Octet: The octet 3D printing infill pattern creates tetrahedral (pyramid-like) volumes inside the part. It is best for parts with large horizontal surfaces. Smaller gaps between the infill walls are possible due to the tapering nature of the pyramid-like volumes. This allows for shorter span distances between infill walls and a lesser chance for the material to sag. Improved top surfaces can therefore be achieved without having to increase the infill density. Figure 4 is an example of an octet infill pattern:

4. Concentric: The concentric 3D printing infill is one of the fastest infill patterns to print, and it uses the least material. However, this comes at the cost of reduced part strength. The concentric pattern is not as strong as the other infill types, especially when loaded in the x or y-directions. Figure 5 is an example of a concentric infill pattern:

5. Lightning: This unique infill type provides the fastest possible print time at the expense of part strength. Supports are added in a lightning bolt structure and only placed where necessary. Parts are shells except where support is needed for horizontal features or internal overhangs. Figure 6 is an example of a lightning infill pattern:

6. Triangular: The triangular 3D printing infill pattern lays down plastic in a triangular grid that crosses over itself at 60-degree angles. This type of infill pattern is best used on parts with large, flat surfaces, and performs similarly to the grid pattern. The triangular infill can cause the nozzle to clog, as its lines criss-cross each other in the same layer. Figure 7 is an example of a triangular infill pattern:

7. Tri-Hexagon: The tri-hexagon is the strongest infill pattern. Like the grid and triangular infill types, it will cross over itself to create a hexagonal pattern interspersed with triangles. Due to the crossing of lines in the same layer, this type of infill tends to clog the print nozzle. Figure 8 is an example of a tri-hexagon infill pattern:

8. Cubic: The cubic infill type creates cubic volumes inside the part. It does this by producing a layered pattern similar to a triangular infill. However, it offsets each subsequent layer to build enclosed cube-shaped volumes in the part. The cubic volumes are oriented with the cube balanced on one corner. Figure 9 is an example of a cubic infill pattern:

9. Grid: The grid is one of the most common infill types. The grid pattern lays down plastic in a cubic grid pattern that crosses over itself at 90-degree angles. This infill pattern is ideally used for prints with large, flat surfaces. Gridded infill patterns can cause nozzle clogging since the lines criss-cross over each other in the same layer. Figure 10 is an example of a grid infill pattern:

10. Cross: The cross pattern creates multiple cross shapes as infill. This 3D printing infill pattern is ideal for flexible part shapes as it allows for the part to bend and twist. It is not very useful for more rigid plastics, however. A 3D version of the cross is also available to add additional strength.  Figure 11 is an example of a cross-infill pattern:

What Does the Ideal Value of the Infill Percentage Depend Upon?

The main determining factor for infill percentage is the type of application for which the part is destined to be used. Prototypes and hobbyist creations rarely need more than 20% infill. Functional parts that will be exposed to mechanical stress loads will typically require infill percentages of 50% or more.

What Is the Recommended Infill Percentage for Other Simple Exposure Objects?

For objects that will not see any significant mechanical load, a fill percentage of 20% is sufficient. It must be noted that the geometry of the part may require a different infill percentage. For example, a flat, horizontal surface may need a denser infill percentage to ensure that the top layer does not sag due to a lack of support. 

How Much Infill Is Required To Achieve Maximum Tensile Strength?

The higher the infill percentage, the higher the tensile strength of the part. It must be noted that infill percentage is not the only factor that determines tensile strength. For example, filament material and print orientation play a major role. FDM parts, in particular, are anisotropic. They are weaker along the z-axis due to interlayer bonding weakness. If an FDM part is loaded in the z-direction, the dominant factor controlling its tensile strength will be the interlayer bonding quality. Infill percentage will have little effect in this case.