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What is Infill in 3D Printing?

Hello Machine Bros!
Have you ever wondered, What is Infill in 3D printing? Well, today we will explain everything related to this topic.

When we talk about Infill, we refer to the plastic material deposited internally in a 3D printed object, which can fulfill several functions. For example:

  • Give weight to the piece.
  • Provide 3D printing support.
  • Give robustness and solidity to the 3D print.

So, let’s get started.

The Definition of Infill

The infill is the internal structure of 3D printing, it is the material that is used to fill the 3D printed parts.

Generally, the infill should not be visible once the model is finished.

Infill in 3D Printing

Infill Role and Importance in 3D Printing

The Infill can fulfill various functions and have different levels of importance or utility in 3D printing.

Next, we show a list that orders the Infill functions from highest to lowest according to the importance given to it:

  1. Add robustness and solidity to the 3D print.
  2. Provide printing support for the upper layers.
  3. Give weight to the 3D print.
  4. Add a different aesthetic level to the 3D prints.
What is Infill in 3D Printing?
Difference between using or not using Infill in a cube

Infill Slicer Configuration Parameters

Next, we will explain the different configurable parameters of Infill in the Slicer Simplify3D.

Adjustable Infill Parameters in Simplify3D
Adjustable Infill Parameters in Simplify3D

Infill Extruder:

This parameter only applies if you have a 3D printer with multiple extruders.

The Infill Extruder option allows us to select with which extruder we want to deposit the filling material.

Internal Fill Pattern

The Internal Fill Pattern option allows you to choose from a variety of fill patterns:

  • Rectilinear
  • Grid
  • Triangular
  • Wiggle
  • Fast Honeycomb
  • Full Honeycomb.

These Infill Types are explained in more depth later in the Infill Types section.

Comparison between two different type of Infill patterns
Comparison between two different type of Infill patterns

External Fill Pattern

External Fill Pattern allows us to choose between two fill patterns of the outer layers.

Among the options we have Rectilinear and Concentric.

Difference Between Rectilinear and Concentric External Fill Pattern
Difference Between Rectilinear and Concentric External Fill Pattern

Interior Fill Percentage

The Interior Fill Percentage parameter is used to adjust the amount of Infill used to fill the 3D print.

The higher the percentage, the more filling the 3D print will have.

We will touch on this topic in greater depth in the Infill Percentage section.

Infill parameters in Simplify3D
Difference between a percentage of Infill 10% and 30%

Outline Overlap

With Outline Overlap we adjust how much we want the external part of the Infill to adhere to the contour of the 3D Print.

This value is entered as a percentage.

(Press play to see the animation)

Comparison between using 10% and 80% in the Outline Overlap parameter

Setting this parameter high can help plug holes in the surface of the outermost layers.

This can be seen in the following image.

Outline overlap parameter simplify3D
Comparison between using 0% and 40% in the Outline Overlap parameter

Infill Extrusion Width

The Infill Extrusion Width option allows you to choose the width of the infill lines.

If for example we place 100%, the infill will have the same width as the outline.

If we put 200%, the infill will have a width twice as large as the outline.

Parameter Infill Extrusion Width
Difference between using 100% and 200% in Infill Extrusion Width

Minimum Infill Lenght

Segments with a total length less than the value that we set in Minimum Infill Lenght will not be considered to place the infill.

This parameter is useful to ignore small spaces where it is not necessary to deposit infill.

Difference between using 2mm and 6mm in Infill Extrusion Width

Combine Infill Every # Layers

This option is used to deposit filling at every certain layer height, to speed up the 3D printing time.

For example, if your Layer Height is 0.1mm, and you decide to combine the Infill every 3 layers, you will end up printing a 0.3mm Infill every three layers.

As with the layer height, the limitation is based on the diameter of the nozzle, the ideal is not to exceed a layer height greater than 80% of the diameter of the nozzle.

For example, if you have a 0.4mm nozzle, you shouldn’t exceed a layer height of 0.32mm.

If you have a 0.4mm nozzle, and you are printing at 0.1mm layer height, you shouldn’t combine more than 3 layers of Infill. With 3 layers you would already be printing the infill at a layer height of 0.3mm.

If you exceed the value, you run the risk that the infill layers will not adhere well to each other and when you exceed the recommended value, Simplify3D will give you a warning message.

For example, suppose we have a 0.2mm layer height set, with a 0.4mm nozzle, and we try to set the Combine Infill Every # Layers value to 3. We would end up having a 0.6mm layer height for the Infill, which exceeds the recommended value for a 0.4mm diameter (0.32mm) nozzle.

If we exceed the recommended value for a 0.4mm nozzle, Simplify3D will give us the following warning message.

Simplify3D error message Unusual Width/Height Ratio
Warning message where Simplify3D tells us that we have chosen a Combine Infill Every # Layers value that exceeds the recommended limits of the “width / height” ratio. This by choosing to combine the infill layers every three layers, having a layer height of 0.2mm, with a 0.4mm nozzle.

We will generally use 1 as the value of this parameter, unless we use a low enough layer height, or a nozzle with a large enough diameter to use another value.

(Press play to see the animation)

Example of what happens when choosing to combine the infill every 3 layers with a layer height of 0.1mm configured

Include Solid Diaphragm Every # Layers

With the Include solid diaphragm every # layers option we can tell the Slicer to 3D print a solid layer in a certain interval of layers.

If we select the number 3 as the value, then we would print two normal layers and then the third layer would be solid. So on until the 3D printing is finished or the configuration is modified.

(Press play to initiate the animation)

Example of what happens when including a solid layer every 3 layers.

Internal Infill Angle Offsets

The Internal Infill Angle Offsets option adjusts the direction in which the internal infill will be printed in 3D.

This parameter is not usually modified, since it is self-adjusting according to the printing pattern chosen in the Internal Fill Pattern.

(Press play to see the animation)

Example of how the value of Internal Infill Angle Offsets changes based on the Internal Fill Pattern parameter.

External Infill Angle Offsets

The External Infill Angle Offsets option adjusts the direction in which the External Infill will be 3D printed. This parameter is not really modified.

The default values of 45° and -45° usually work quite well.

This parameter only takes effect when a Rectilinear external fill pattern is chosen in External Fill Pattern.

In contrast, if you choose a Concentric external fill pattern, the External Infill Angle Offsets function no longer has any effect.

External Infill Angle Offsets Simplify3D
Default and commonly used value in External Infill Angle Offsets

(Press play to see the animation)

Difference between using only (45°) and using (45° and -45°) in the External Infill Angle Offsets parameter.

Infill Percentage

The percentage of Infill determines the amount of filling that we will use, the higher the percentage of Infill, the more resistant, heavier, and has greater internal support.

As a disadvantage, more material is used, and the 3D printing time increases.

Simplify3D explains that for them, the Infill percentage expresses the density of the filling of a 3D print, that is, if you have an Infill percentage of 20% configured, 80% of the interior of the piece will be empty.

Infill percentage
Difference between using a Grid pattern infill at 20% and 70%

Table showing the difference between using a Grid pattern infill at 20% and 70%

InfillGrid 20%Grid 70%
3D printing time2h y 42m5h y 52m
Filament lenght8415.9mm22495.2mm
Filament weight25.30g67.63g
Material cost0.76USD2.03USD

If we want a more resistant 3D print, we use a greater amount of Infill, if you only want an aesthetic piece, you can decrease the Infill.

The Infill also fulfills the function of serving as a support, so, keep this in mind if you want to reduce it.

Next, we will show you an example of a cube, which, if we were to 3D print it without enough Infill, the upper layers would look bad or collapse since it would not have the proper internal support.

(Press play to see the animation)

Example of a cube that would be badly printed, since the upper layers do not have the necessary internal support generated by the Infill

Percentage of Infill Commonly Used

If you do not know what percentage of Infill to use, a value between 8% and 20% usually works for general 3D prints that do not need to be very resistant.

As for the fill pattern, the most common for a basic 3D printing is to use Rectilinear or Grid.

Later in the section Infill Types we explain in greater depth about Infill patterns.

3D Printing Infill Types

Rectilinear

The Rectilinear pattern is configured by default in Simplify3D.

With this fill pattern, squares are formed inside the piece.

The difference of this fill pattern with the Grid, is that when we use Rectilinear a diagonal is printed each layer. With Grid, squares are formed on all layers.

(Press play to see the animation)

Rectilinear fill pattern

Grid

With the Grid pattern, squares are also formed inside the 3D print.

The difference of this fill pattern with the Rectilinear, is that when we use Grid, the squares are formed in all the layers. With Rectilinear a diagonal is printed each layer.

(Press play to see the animation)

Grid fill pattern

Triangular

The Triangular fill pattern forms triangles inside the 3D part.

(Press play to see the animation)

Triangular fill pattern

Wiggle

The Wiggle fill pattern seeks to offer a different aesthetic during 3D printing (Remember that generally the infill cannot be seen once the part is ready).

Using this fill forms wavy lines inside the 3D printed part.

(Press play to see the animation)

Wiggle fill pattern

Fast Honeycomb

With the Fast Honeycomb fill pattern, a honeycomb structure is formed on the inside of the 3D printed part.

The difference of this filling pattern with the Full Honeycomb, is that when we use Fast Honeycomb, the honeycomb structure finishes forming every two layers. With Full Honeycomb the honeycomb structure is completed in each layer.

(Press play to see the animation)

Fast Honeycomb fill pattern

Full Honeycomb

With the Full Honeycomb fill pattern, a honeycomb structure is also formed on the inside of the 3D printed part.

The difference of this fill pattern with the Fast Honeycomb, is that when we use Full Honeycomb, the honeycomb structure is completed in each layer.

Full Honeycomb fill pattern

Here’s a comparison of these Infill patterns mentioned earlier.

Infill pattern comparison
Comparison of Infill patterns in 3D printing
Comparison of Infill patterns in the first layer
Comparison of Infill patterns in the second layer

Multiple Infill Parameters With the “Variable Settings Wizard” Option in Simplify3D

With the Variable Settings Wizard option, it is possible to use multiple Infill settings depending on the layer height.

This would allow us to make the pieces more resistant in certain sections that we consider necessary.

(Press play to activate the animation)

Use multiple infill settings in one 3D print.

You must bear in mind that you cannot aspire to have a very low infill, and then a very dense infill, because the dense infill will have no support on which to print, that is, it would be printed practically in the air.

Create a Fully Solid 3D Model with the Include Solid Diaphragm Option

If for some reason you need a 3D model to be totally solid there are two options:

1- Set the Infill to 100%

2- Use the Include Solid Diaphragm option

We prefer to use the second option.

We set the Include Solid Diaphragm parameter to 1, in this way all the layers of the model will be solid.

In the following example you will notice how we can use Include Solid Diaphragm in conjunction with Variable Settings Wizard to make the parts of a model that we consider potentially fragile solid.

(Press play to start the animation)

Making a certain part of a fully solid model using Include Solid Diaphragm in conjunction with Variable Settings Wizard

The Strongest Geometric Shape

For engineering and science in general, the strongest geometric shape is the triangle.

For this reason, you may notice that in civil engineering and architectural works where great resistance is required, this geometric pattern is usually used.

Next, we will show you some examples of the aforementioned.

The strongest 3D printing Infill
Example of a triangular mesh
The strongest geometric shape
Example of a dome with a triangular structure
Example of a triangular structure
Example of a triangular structure
Bridge over the Kama River (Russia), for the Trans-Siberian Railway using a triangular structure
Bridge over the Kama River (Russia), for the Trans-Siberian Railway using a triangular structure
The London Eye uses a triangular structure.
The London Eye uses a triangular structure.

In the infill, will the triangle pattern be the strongest? We will see this later in the mechanical test carried out in the section Comparison of Resistance to Mechanical Stress with Different Types of Infill.

3D Printing Speed Comparison Using Different Infill Types

Simplify3D explains that for them the Infill percentage expresses the density of the filling, that is, if you have an Infill percentage of 20% configured, 80% of the interior of the piece will be empty.

But there is a certain discrepancy between this theoretical concept that they mention, and the results produced by their own software.

If the density were the same, having a constant Infill percentage, the final weight of the piece should be the same regardless of the pattern used, but for some reason this does not happen.

We have to adjust the Infill percentage based on the chosen 3D printing pattern so that the weight remains relatively constant.

We do not know exactly why this phenomenon occurs, but there could be two possible explanations:

  1. There is an error in the weight calculation.
  2. The percentage of the infill does not keep the density of the infill constant when changing the 3D printing pattern.

Well, these are just hypotheses. Therefore, we will do the analysis from both perspectives.

First, we will use the weight of the 3D print expressed in grams as a common factor.

Let’s compare how fast a cube would print using different print patterns.

All these cubes will weigh approximately the same, therefore, they will theoretically carry the same amount of material (It will not be able to be exact because it is not possible to choose a percentage of Infill with decimals).

The only value that we will alter between the cubes will be the percentage of Infill, so all of them can weigh the same.

Comparison of 3D printing speed based on different Infill patterns with low Infill percentage
Comparison of 3D printing speed based on different Infill patterns with low Infill percentage

Table comparing the results using low percentage of Infill

Pattern typeRectilinearGridTriangularWiggleFast HoneycombFull Honeycomb
% Infill10%8%9%10%10%11%
Weight (g)15.17g14.81g14.92g14.73g14.89g14.90g
Printing time1h y 5m1h y 4m1h y 5m1h y 8m1h y 11m1h y 8m
Speed (g/min)0.23g/min0.23g/min0.23g/min0.22g/min0.21g/min0.22g/min
Comparison of 3D printing speed based on different Infill patterns with high Infill percentage
Comparison of 3D printing speed based on different Infill patterns with high Infill percentage
Pattern typeRectilinearGridTriangularWiggleFast HoneycombFull Honeycomb
% Infill50%48%47%51%54%56%
Weight (g)40.64g40.71g40.69g41.04g40.55g40.36g
Printing Time2h y 30m2h y 31m2h y 31m4h y 34m4h y 16m4h y 1m
Speed (g/min)0.27g/min0.27g/min0.27g/min0.15g/min0.16g/min0.17g/min
Table comparing results using high percentage of Infill

NOTE: The value “Speed (g/min)” was obtained by dividing the grams that the piece weighs by the time expressed in minutes that it would take to 3D print it.

With the data obtained, we can conclude that the 3D printing pattern does not seem to greatly affect 3D printing times when we use low infill percentages (between 8% and 11%).

But when we use high percentages of Infill (between 47% and 56%), the difference in 3D printing times depending on the chosen printing patterns becomes very noticeable.

By using high infill percentages, the patterns that allow faster printing are: Rectilinear, Grid and Triangular, and the patterns that end up resulting in slower 3D printing are: Wiggle, Fast Honeycomb and Full Honeycomb.

This is based on the fact that we use the same amount of material in the pieces, and not focusing on the percentage of the infill.

This data has some logic, since patterns such as Rectilinear, Grid and Triangular are only printed by drawing straight lines.

On the contrary, patterns like Wiggle, Fast Honeycomb and Full Honeycomb require a constant change of direction, therefore, it is logical to think that these take longer to be 3D printed.

Now we will use the percentage of Infill as a common factor, we are going to compare how fast a cylinder would print using different printing patterns and leaving the percentage of Infill constant.

Comparison of 3D printing speed based on different infill patterns with a constant infill percentage
Comparison of 3D printing speed based on different infill patterns with a constant infill percentage

Table comparing results using constant infill percentage

Pattern typeRectilinearGridTriangularWiggleFast HoneycombFull Honeycomb
Infill %50%50%50%50%50%50%
Weight (g)31.71g32.28g32.70g31.78g30.30g29.34g
3D Printing Time1h y 56m1h y 58m2h y 1m3h y 30m3h y 6m2h y 48m
Speed (g/min)0.27g/min0.27g/min0.27g/min0.15g/min0.16g/min0.17g/min

The results were the same as when we did the study, keeping the weight constant.

The patterns that allow faster 3D printing are: Rectilinear, Grid and Triangular and the patterns that end up resulting in slower printing are: Wiggle, Fast Honeycomb, and Full Honeycomb.

Comparison of Resistance to Mechanical Stress with Different Types of Infill

To carry out these mechanical resistance tests, we design test specimens with the different types of Infill to see which of all is the one with the highest mechanical resistance.

In the following video is the mechanical test and its conclusions, if you do not want to see the video, then read our summary below.

Video of the mechanical test and its respective conclusions (Remember to activate the subtitles if you do not have them already activated)

Summary of the Mechanical Test

We design the following test specimen.

Mechanical test for infill patterns
Image of the test specimen in SolidWorks
Mechanical stress on infill patterns
Test specimen dimensions

First, we 3D printed several test specimens trying to keep the weight constant, so, small variations of the infill were made.

These specimens were subjected to a tensile test, and these were the results:

Result of the mechanical test of infill
Results of the mechanical test trying to keep the weight constant

Then we 3D print several test specimens keeping the infill constant.

These test specimens were subjected to a tensile test, and these were the results:

Best 3D Printing Infill
Results of the mechanical test keeping the infill constant

In both tests, the test specimens with the slowest printing patterns were the most resistant (Wiggle, Fast Honeycomb, Full Honeycomb).

In both studies the most resistant pattern was Fast Honeycomb.

Does this mean that the most resistant geometric figure is not the triangle?

This is NOT the conclusion we reached and there are several factors to consider.

Let’s start for example with Wiggle, this pattern had good results, but it is generally described as a purely aesthetic pattern. Look at the following image.

Wiggle pattern
Wiggle oriented in two different ways in a test specimen

If we had 3D printed Wiggle with the lines perpendicular to the pulling force, the result would have been very different.

Wiggle does NOT offer strength and stability in all directions.

The number of printing lines that have the same direction (or with an approximate direction) to the direction of the force has a very important influence.

The test specimen shown below, with a single print line in the direction of force  is less resistant than a test specimen with 3 lines of printing in the direction of force.

Mechanical forces on Infill Patterns
Test specimen with a single printing line
What's the strongest Infill?
Test specimen with three printing lines

For this reason, it does not seem fair to compare this Triangular infill pattern with the Fast Honeycomb

Infill Triangullar Pattern
Triangular Pattern
Fast Honeycomb Infill pattern
Fast Honeycomb pattern

Simplify3D says to parameterize the percentage of the Infill based on the density of the filling, which is the same as saying that they take into account the volume of material they use from Infill.

Although in the same way it does not seem to have congruence what they say, since, when changing the fill pattern, but maintaining the same Infill percentage, the weight also changed. And this should not happen.

It may be that a fairer comparison is to compare the area that the infill covers, and not the volume. Well, it is not the same to want to compare a test specimen with 100 triangles, with another test specimen with 10 thousand squares.

For this reason, it was possibly a bit stronger Fast Honeycomb than Full Honeycomb in the two studies.

Patterns like Full Honeycomb focus on depositing the same print lines on all layers, for this reason, it occupies the same volume as Fast Honeycomb, but leaving more uncovered area. Remember Fast Honeycomb swaps the print lines on each layer.

Based on this hypothesis, we did another mechanical test using more triangular patterns with different Infill percentages, these were the results:

Different 3D Printing Infill Patterns
Mechanical test results using more triangular patterns

Conclusions of the Mechanical Test

Note: The conclusions were mentioned in the video, if you already saw it, you can go to the next section.

Visually, it appears to have a similar Fast Honeycomb fill area at 50%, with Triangular (between 70% and 80%). Furthermore, the results obtained are similar.

But the approximation of the area was only visual, therefore, it is difficult to reach an accurate conclusion with these results, so it is still a hypothesis, although quite reasonable.

It is also true that by using Triangular at 70%, we end up wasting more material than by using Fast Honeycomb at 50%.

Again, the question arises, are triangles then the most resistant figure? So far yes, science has already proven it and engineers and architects have been using this figure for decades to build resistant and stable structures.

What about Honeycomb? This geometric shape is also widely used in engineering for the creation of structures.

In certain occasions, Honeycomb is more profitable than Triangular, this because under specific conditions it is easier to create a surface mesh with Honeycomb than with Triangular.

There are times where “many” triangles are required to cover a surface, in these cases it is more profitable to use Honeycomb to create the mesh or structure.

For this reason, we generally need more 3D printing filament when using Triangular than Fast Honeycomb infills.

We can conclude that the following items play a fundamental role in terms of the resistance that the pieces will have:

  1. The percentage of the infill
  2. The printing lines in the direction of the force
  3. The number of perimeters
  4. Layer height
  5. The fill pattern

among other things.

Which Infill Should you Choose for your 3D Printing?

That depends! Is your 3D print gonna be exposed to mechanical stress? is it gonna be just a decoration? next, we bring you the answer for those questions.

3D print that Won’t be Subjected to Mechanical Stress

It will be enough to use a Rectilinear or Grid fill pattern between 8% and 20% (It can be less or more).

The important thing is that the infill is enough to support the upper layers, that is, that it serves as a base, otherwise the upper layers could be printed in the air.

3D Print that Will be Subjected to Intermediate Mechanical Stress

If you want to save 3d printing filament but spend a little more time on the 3D printing, you can choose Fast Honeycomb. With a percentage between 40% and 60% it could be enough (It can be less or more, it will depend on your needs)

If you want to spend more filament but save a little on 3D printing time, you can choose Triangular. With a percentage between 60% and 80% it could be enough (It can be less or more; it will depend on your needs).

With Triangular you could get good resistance in more directions than with Fast Honeycomb, since remember that Triangular creates print lines in several directions (this at the cost of spending more material).

3D Print that Will be Subjected to Great Mechanical Stress

You could use Triangular infill between 90% and 100%.

You could also use the Include Solid Diaphragm option and create a totally solid model.

This is explained in Creating a Fully Solid Model with the Include Solid Diaphragm option.

Common Failures About the Infill in 3D Printing

Weak Infill

Weak Infill 3D Printing
Weak Infill

If you notice that your Infill seems weak or resembles the one in the photo, you can try the following possible solutions:

  1. Try using another fill pattern, it is less common to see this type of failure in patterns such as Grid, Triangular and Full Honeycomb.
  1. Try reducing the printing speed. You may be printing too fast, not giving the extruder time to properly deposit the filler.
  1. Try increasing the extrusion width of the Infill. With the Infill Extrusion Width option, you can try increasing it by 10% each time until getting the desired results.

For example, if you previously had this value at 100%, raise it to 110% and try again, if you do not notice an improvement, increase it to 120%, and so on.

Infill Percentage is Too Low

If we use a very low infill percentage, we may encounter the following drawbacks:

Gaps in Top Layers Infill
Gaps in Top Layers
Gaps in Floor Corners
Gaps in Floor Corners

These two faults can be symptoms that you are using a very low infill percentage.

If you have already tried other possible solutions, try increasing the percentage of the infill and evaluate the results.

Gaps Between Infill and Outline

Gaps between infill and perimeter
Gaps between infill and perimeter

If you notice these gaps between the infill and the perimeter, you can try the following possible solutions:

  1. Try increasing the Outline Overlap parameter, this is explained in the Infill Configuration Parameters section in Simplify3D. Even in that same section we explained that with the Outline Overlap setting we can “cover holes in the surface of the outermost layers”.
  1. Try reducing the printing speed, it is possible that you are 3D printing too fast, and do not give the extruder time to correctly deposit the filler.

Note: All these problems with their solutions can be found at the Simplify3D Troubleshooting.

The Infill Function When Wanting to Drill and Screw a 3D Printed Part

Have you wondered, how to insert a screw in a 3D print?

The infill plays an essential role if you want to pierce a 3D printed part and place a self-tapping screw (for instance) since if you don’t have enough infill, the screw will have nowhere to hold onto.

Take this into account when 3D printing a part in which you need to place a screw of this type. In this case, is recommended to have a high percentage of Infill.

Conclusions About the Infill in 3D Printing

In this article we explain about the types of Infill in 3D printing, the resistance they offer, the times and speed of 3D printing, as well as some secrets and tricks that we apply.

In the end, we can assure you that the Infill is another fundamental part of 3D printing, and the success of a good 3D print can depend on it.

The Infill greatly influences the finish of a 3D print, because the Infill serves as a support for the upper layers, or the mechanical resistance that your part will have (the latter in case you 3D print a functional model).

If you are new to the Slicer Simplify3D, we recommend you the article Beginner’s Guide of Simplify3D

If you already know Simplify3D and are looking for more advanced information, check out the Advanced guide of Simplify3D.

It has been a pleasure for us to write this article for you and we hope you found the answers about What is Infill in 3D Printing. We are very motivated to share information with you on this subject that we are so passionate about.

Any questions you have, do not hesitate to leave it in our comments section, as well as any contribution or suggestion you wish to make, we are here to grow together in this wonderful world of 3D printing.

Cheers

Until the next one Machine Bros!

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