Infill in 3D Printing: What It Is and Why It Matters

The internal structure of a 3D-printed object—called infill—plays a key role in successful printing. This pattern between the outer shells affects your object's strength, weight, and material use. The right infill settings can make the difference between a fragile model and a durable, functional part while helping you balance print time and material consumption.

What Is Infill in 3D Printing?

Infill is the internal structure that fills the space inside the outer shell of a 3D-printed object. Think of it as the skeleton that supports your print from within. When you slice a 3D model for printing, the software creates this internal framework according to your settings, generating patterns that provide structural support without making the object completely solid.

The infill typically consists of repeating geometric patterns that connect the inner walls of your print. These patterns use varying amounts of material depending on the density setting you choose.

How Infill Affects Your Prints

Infill directly influences several key aspects of your finished print:

• Strength: Higher infill density creates more internal connections, resulting in stronger prints that can withstand greater stress and pressure.
• Weight: The amount of infill determines how heavy your final object will be. Lower density means a lighter print.
• Material Usage: More infill requires more filament. Reducing infill density is one of the most effective ways to save material and reduce printing costs.
• Print Time: Dense infill patterns take longer to print because the nozzle must travel more to deposit all that extra material.

Solid vs. Hollow vs. Infill

Using infill offers significant advantages over both completely solid and hollow prints:

A well-chosen infill setting gives you the best of both worlds—strength where needed without excessive material use or print time.

Types of 3D Printing Infill Structures

Common Infill Patterns

The pattern you select for your infill greatly influences your print's performance. Modern slicing software offers several pattern options, each with distinct properties:

Grid: This simple pattern creates perpendicular lines that form squares. The grid pattern is quick to print and provides balanced strength in two directions (X and Y axes). It's an excellent all-purpose option for many basic prints.

Rectilinear: Similar to grid but with parallel lines that alternate direction between layers. This pattern offers good strength with minimal material and prints quickly. It's ideal for drafts and prototypes where print speed matters more than maximum strength.

Triangular: Forms triangles throughout the interior of your print. This pattern distributes force more evenly than grid patterns and resists bending from multiple directions, making it suitable for functional parts that need consistent strength.

Honeycomb: Creates hexagonal cells resembling a beehive. This pattern provides exceptional strength-to-weight ratio and excellent resistance to compression. While it uses more material and takes longer to print than simpler patterns, honeycomb infill is perfect for parts that need to bear weight.

Gyroid: An organic, wave-like continuous structure. The gyroid pattern offers uniform strength in all directions (isotropic) and allows air and fluids to flow through the print. It's particularly useful for flexible materials and applications requiring unique mechanical properties.

Pattern Performance Characteristics

Strength Distribution

Different patterns distribute strength in different ways:

• Grid and Rectilinear: Strongest along the X and Y axes, weaker along Z
• Triangular: More balanced strength in all horizontal directions
• Honeycomb: Excellent compression strength with good load distribution
• Gyroid: The most uniform strength in all directions, including Z-axis

Flexibility and Material Considerations

The infill pattern affects how your print flexes under pressure:

• Gyroid: Provides the most consistent flexibility and works exceptionally well with TPU and other flexible filaments
• Honeycomb: Offers controlled flex under pressure with good recovery
• Grid/Rectilinear: Creates more rigid structures with less give
• Triangular: Provides rigidity with balanced resistance to bending

Print Speed and Efficiency

Your choice of pattern significantly impacts print time:

• Rectilinear: Usually the fastest to print
• Grid: Quick and efficient
• Triangular: Moderate print time
• Honeycomb: Slower due to frequent direction changes
• Gyroid: Often the slowest pattern because of its complex geometry

For time-sensitive projects, simpler patterns like rectilinear or grid will reduce print duration. When strength is the priority, the extra time required for honeycomb or gyroid patterns is usually worthwhile.

Infill Density in 3D Printing

What Infill Percentage Means

Infill density is the percentage of internal space filled with material in your 3D print. It ranges from 0% (completely hollow) to 100% (completely solid).

Low Density (10-20%)

Low density infill creates prints that are lightweight and quick to produce. The internal structure is sparse but provides enough support for the top layers of your print. This density range is ideal for decorative models, prototypes, and other non-functional items where strength isn't a primary concern. The minimal material usage makes low-density prints economical, especially for larger objects.

Medium Density (25-40%)

Medium density infill strikes a balance between strength and material efficiency. This range provides reasonable durability for general-purpose items while keeping printing time and material costs moderate. Household objects, containers, and light-duty functional parts typically perform well with medium density infill. Most everyday 3D printing projects fall into this category, offering good results without excessive material use.

High Density (50-100%)

High density infill produces strong, robust parts capable of withstanding significant stress. As you approach 100%, prints become nearly solid and maximize strength. This range is necessary for mechanical components, tools, and items that need to bear weight or resist breaking under pressure. The trade-off is substantially increased material consumption and longer print times. Reserve high-density settings for parts where strength is critical to functionality.

How Density Affects Your Prints

It Determines Material Consumption

Higher infill means more filament used. A 20% infill might use only a third of the material needed for a solid print, saving both material and money. For large prints, even small reductions in infill percentage can lead to significant savings.

It Controls Print Duration

Infill density directly impacts how long your print takes to complete. Low-density prints (10-20%) finish much faster than high-density prints (50%+). This happens because the printer needs to trace more paths and deposit more material with higher infill settings.

It Defines Structural Strength

The strength of your print increases with higher infill density. Parts with 50% or greater infill can handle significant stress and weight. However, strength doesn't increase linearly—the difference between 80% and 100% infill is often minimal, while using much more material.

Factors That Influence Your Infill Choice

While previous sections covered what infill patterns and densities are available, this section focuses on how to make the right selection for your specific situation.

Purpose of Your 3D Print

Let your print's function guide your infill decisions:

For Specialized Applications

Beyond basic strength considerations, think about unique requirements. Parts that need to absorb vibration benefit from gyroid infill at medium densities. Objects designed to float require very low infill percentages. Items that will be exposed to high temperatures perform better with higher density infill for improved heat distribution.

Environmental Factors

Consider where and how your print will be used. Outdoor items need water resistance, which often means higher infill density to prevent water infiltration. Parts exposed to UV light may degrade over time, potentially requiring additional strength from the start.

Material-Specific Considerations

Different filaments require different infill approaches:

PLA prints cleanly with most patterns but can be brittle with low infill densities. Its minimal shrinkage makes it suitable for precise geometric patterns.

ABS and PETG exhibit more thermal movement during cooling. These materials benefit from infill patterns that accommodate expansion and contraction, with gyroid being particularly effective at preventing internal stress buildup.

Flexible Filaments (TPU/TPE) often perform poorly with complex infill patterns that restrict their natural movement. Simpler patterns with moderate spacing allow the material to maintain its flexibility properties.

Composite Filaments containing wood, metal, or carbon fiber particles can cause accelerated nozzle wear. For these materials, using efficient patterns at moderate densities extends nozzle life.

Printer Capabilities and Limitations

Your hardware directly impacts what infill settings are practical:

Print Head Dynamics

Bowden extruder setups may experience more difficulty with rapid direction changes required by complex infill patterns. Direct drive systems generally handle intricate infill patterns more precisely.

Nozzle Size Considerations

Larger nozzles (0.6mm+) print faster but create coarser infill structures. When using larger nozzles, you'll need wider spacing in your infill pattern to avoid over-extrusion at intersection points.

Cooling System Effectiveness

Printers with single-sided cooling fans may struggle with higher infill densities, especially in enclosed areas where heat buildup occurs. In these situations, reducing infill density or increasing minimum layer time can improve results.

Processing Power Constraints

Older printer control boards sometimes lack the processing power to handle complex patterns at high speeds. If your printer stutters during intricate infill sections, simpler patterns may be necessary regardless of their structural properties.

Master Infill Settings for Better 3D Prints!

Choosing the right infill settings is key to successful 3D printing. With proper patterns and densities, you can create prints that balance strength, weight, material usage, and print time. Remember that different projects need different approaches—decorative models work fine with 10-20% infill using simple patterns, while functional parts may need 50% infill with stronger structures. Try various combinations and adjust based on your specific printer and materials. These small changes to your print's internal structure will significantly improve your results.