Optimizing Infill for Better 3D Prints

Infill is one of the most important settings in 3D printing that determines the strength, weight, print time and material usage of a printed part. Understanding how to optimize infill can help produce stronger prints faster and with less material.

What is Infill in 3D Printing?

Infill refers to the interior structure that fills the inside volume of a 3D printed model. It is usually printed in a grid or lattice pattern rather than printing a completely solid interior.

The infill percentage is the amount of material used on the inside compared to a completely dense fill. A 10% infill means only 10% of the interior volume is filled with material, while the rest is empty space.

Infill serves several purposes:

• It provides internal structure and strength to the printed part. Without infill, the model would be weak and fragile.
• It supports the top layers and helps resist forces on the part. Denser infills provide more rigidity and strength.
• It reduces weight and material use compared to a completely solid interior. Less infill uses less filament.
• It reduces print times compared to a completely solid model which would take longer to print.

Common Infill Patterns

There are several common infill patterns used in 3D printing:

• Grid – This is the most common pattern and generates a lattice by printing back and forth lines in alternating directions. It provides good strength and printability.
• Lines – This simple pattern prints parallel lines across the layer with no alternating directions. It has less strength but prints quickly.
• Triangles – This pattern prints triangles in alternating directions for added strength over lines. It has good strength-to-print time ratio.
• Cubic – This infill prints interconnected cubic shapes for high strength but uses more material and print time.
• Octet – A more complex infill that prints intersecting octagons in alternating x/y directions. Provides excellent strength with moderate print times.
• Concentric – Prints infill in concentric rings originating from the center of the part. This is best for circular or cylindrical objects.
• Zig Zag – Prints infill by zig-zagging back and forth across each layer. This adds some extra strength over standard grid.
• Gyroid – A complex wavy infill pattern that provides excellent strength and lightweight properties. It can be tricky to print but gives amazing performance when done right.

How Infill Percentage Impacts 3D Printed Parts

The infill percentage directly affects several properties of the printed part:

Strength – More infill means a stronger part that can withstand higher stresses and forces without breaking. High infill percentages above 30% dramatically increase rigidity and load capacity.

Weight – More infill uses more material and increases the weight of the printed part. Low infill percentages below 20% are great for lightweight prints.

Print Time – Higher infill takes longer to print all that added material inside the model. Reducing infill can significantly speed up print times.

Material Usage – Obviously more infill uses more filament to print. Low infill percentages can greatly reduce material consumption.

Surface Quality – Low infill can cause the top layers to sag or deform, reducing surface finish. More infill provides better support for top layers.

Cost – More material used means higher costs. Reducing infill is an easy way to reduce the cost of expensive exotic filaments like carbon fiber or glow-in-the-dark.

Infill Recommendations for Strong Functional Parts

For strong functional prints like tools, brackets, mechanical parts, or load-bearing components, follow these infill recommendations:

• Use a minimum of 20% infill, and up to 40% for high-stress applications. Anything lower starts to impact strength.
• Opt for grid, cubic, zigzag, or gyroid infill patterns. These provide excellent layer adhesion and resilience under load.
• Use at least 3 solid top and bottom layers to reinforce the part surfaces. Slow down printing on these layers for best surface quality.
• Set infill overlap to 15-25% so it bonds well with the perimeter shells for better strength. Too little overlap can cause weak points.
• For curved surfaces, use concentric infill to provide equal strength in all directions.
• When printing at layer heights over 0.2mm, increase infill by 5-10% to account for the weaker extrusion bead strength at wider layers.
• Orient the part so the load lines up with the print layers as much as possible. Vertical columns provide better strength than horizontal spans across layers.
• Avoid using 0% infill as this results in a weak surface shell that is prone to cracking under stress. If minimizing weight, use 10-15% infill instead.

Reducing Infill for Faster, Cheaper Prints

For non-functional display models, prototypes, or other applications where strength is not critical, minimizing infill provides major benefits:

• Reduce infill to 10-15% for many display models and prototypes. This saves considerable print time and filament use while still providing basic structural rigidity.
• Prints intended to simply demonstrate shape and form can use 5% infill or even less. This greatly speeds up printing.
• Set infill pattern to grid or lines for fastest printing when strength is not important. Avoid slower patterns like cubic.
• Disable top/bottom infill and use 2-3 solid layers for a shell. Avoid over-reinforcing the top at the expense of print time.
• For vase mode prints with zero infill, use at least 5 perimeter walls to create enough strength while saving filament.
• When reducing infill, orient and position the part to avoid thin sections that may deform easier under gravity loads.
• Increase print cooling to help bridging across thin sections with low infill. Slower speeds also improve bridging.
• Avoid any horizontal bridging spans longer than 5-6mm to prevent sagging, even when well-cooled. Break up the top layers with infill for longer spans.

Finding the Ideal Infill Balance

Determining the right infill percentage and pattern is an art that balances strength, weight, print time, and cost. The ideal infill settings depend heavily on the application and specific needs of the part.

For functional applications demanding performance, don’t be afraid to use 40-50% infill or higher to guarantee the required strength at the cost of increased print time.

For non-critical display models, 10% infill may be perfectly adequate to visually demonstrate the design intent while minimizing material and printing faster.

Finding the ideal middle ground between these extremes – the “sweet spot” of infill – comes down to understanding exactly which properties are most important for the specific application and use case. With experience printing various parts, you’ll learn how to strike the right balance for your needs.

By considering all the impacts infill has on printed parts, both positive and negative, you can learn to strategically optimize this setting and gain much better results from your 3D printer. Dialing in the right infill truly unlocks the full potential of your printer.