3D Printing Infills Explained With Examples
Learn about the importance of infill in 3D printing design and see examples of the different types of infill patterns.
At Xometry, we offer different infill options for our FDM 3D prints. 3D printing infill refers to the internal structure that fills the volume of a 3D-printed part. The purpose of infill is to optimize and balance part weight, strength, and printing time. These internal structures, or infill patterns, can be configured to many different types of shapes and designs. Many of these designs are standardized in slicing software and some are better for certain situations than others.
In this article, we will define 3D printing infill, discuss how to select the correct infill pattern and density and describe the various infill patterns. We will primarily focus on infills often seen with slicing software designed to work with desktop FDM machines; if you are looking to learn more about the infill options Xometry offers, you can check out this short article: Comparing Infill Options for FDM.
What Is Infill in 3D Printing?
“Infill” in 3D printing refers to the internal patterns found inside most 3D printed parts made via the fused deposition modeling process. Parts made by some manufacturing processes, like injection molding, must be made either completely solid or completely hollow. FDM parts, on the other hand, can be made with a variety of structural patterns that partially fill the space inside the outer printed walls. Using infill patterns is common with 3D printing because they can be used to save time and money by minimizing material usage. In many cases, a fully solid part isn't needed to maintain the structural integrity of a part. With that said, there are plenty of 3D printing technologies where printing solid is the norm. For more information, see our guide on Everything You Need to Know About 3D Printing.
The image below shows the three main infill options Xometry offers; solid (left), light (middle), and ultralight (right).
The Purpose of Infill in 3D Printing
The purpose of Infill in 3D printing is to save both printing time and material by creating a lattice structure inside a 3D-printed part. Printing fully dense parts is often unnecessary and a waste of material. Infill can be strategically used to provide strength where in-service loads on the part are the highest. The greater the percentage of infill, the higher the density of the part.
A typical FDM 3D printed part will have an outer shell with a predefined thickness. The infill structure is completely enclosed by this outer shell and is not visible when the part print is complete. The infill will be evenly distributed throughout the part. 3D printing infill is normally printed at higher speeds than the outer shell to save time. The infill print lattice is also typically not as thick as the shell. There are many different infill patterns to choose from, and each have their own advantages and disadvantages.
What Are the Different Types of Infill in 3D Printing?
There are many different types of 3D printer infill. All achieve the same purpose of reducing print time and material usage. Below are some of the most common 3D printing infill patterns in use today:
1. Line: Line infill consists of multiple parallel lines per layer. Each layer crosses over the previous one at a 90-degree angle. Unlike other patterns, the lines don’t cross over each other on the same layer. This strengthens the part in two dimensions. Line infill is marginally quicker than grid and triangular patterns. Below is an example of line infill:
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. Below is an example of a gyroid infill pattern:
3. Concentric: The concentric 3D printing infill is one of the fastest infill patterns to print, and it uses a minimal amount of 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. You can see the concentric infill pattern in the image below:
4. 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 with this infill pattern are essentially shells except where support is needed for horizontal features or internal overhangs. The image below shows what the lightning infill pattern looks like:
5. 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. Be warned, though; the triangle infill is known to have more nozzle clogging concerns, as its lines crisscross each other in the same layer. You can see a triangle infill pattern in the image example below:
6. Tri-Hexagon: The tri-hexagon is one of the strongest infill patterns. 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 also tends to lead to clogs in the print nozzle. The image below shows an example of a tri-hexagon infill pattern:
7. 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. Below is an example of a cubic infill pattern:
8. Grid: The grid is one of the most common infill types and most similar to what we at Xometry most regularly use in our FDM prints. The grid pattern lays down material 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 sometimes cause nozzle clogging with desktop FDM printers since the lines crisscross over each other in the same layer. The grid infill pattern can be observed in the image below:
9. Honeycomb: As the name suggests, the honeycomb infill pattern mimics the structures found in bee hives. It consists of hexagons connected by thin walls. This is a very efficient infill pattern with good strength characteristics and works well for parts that need to be strong, dimensionally stable, and durable. You can see an example of the honeycomb infill in the image below:
Choosing the Ideal Infill Percentage Value
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. At Xometry, we offer a "Solid" infill, which is essentially a 100% infill. It should be noted that even with completely solid infills, FDM parts will still exhibit some degree of porosity due to microscopic gaps between the printed layers.
The higher the infill percentage, the higher the part's tensile strength. Keep in mind that infill percentage is not the only factor that determines this value. Material choice and print orientation play major roles in tensile strength. FDM parts, in particular, are anisotropic. They are weaker along the z-axis since bonding is weaker between layers than on the same layer. We recommend orientating load-bearing features along the xy plane when possible to take advantage of the increased bonding strength in this direction.
An infill percentage of 20% is usually sufficient for objects that will not see any significant mechanical load. Certain geometries may warrant different percentages. 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 To Choose the Best Type of Infill
The steps in choosing the best type of infill are:
- Consider your part requirements and their application. For example, will it be exposed to mechanical stresses and thus must have a strong and dense infill, or will it just be a model for display purposes that can get away with a more sparse infill?
- Assess your resources, including the available material and the time you can spend per part. Denser and more complex infill patterns can be beneficial. However, they can also consume more material and add time to a print.
- Shortlist the infill patterns that match your requirements and resources.
- From this narrowed list, you can select a final infill pattern for your part. You may also want to print the same part with a few different types of infill patterns and see which performs best for your application, keeping in mind the amount of material used and time spent per print.
Choosing the best infill pattern is often a trial-and-error process. We recommend doing a trial or test print on a small part to determine the best settings. When in doubt, sticking with simple patterns like grid, line, or honeycomb is a good place to start.
How Xometry Can Help
Hopefully now you have a clearer idea of which infill to use and when. If you have an upcoming 3D printing project, Xometry offers a wide range of industrial-grade services you can take advantage of, including metal and full-color 3D printing processes! Best of all, most projects quote instantly, giving you price and lead times within seconds. Get started by uploading your 3D files to the Xometry Instant Quoting Engine® today!
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