100% Infill 3D Printing: Crush Loads & Impact Uses

This article explains what 100% infill means for 3D printed parts under crush loads and impacts, and gives five practical uses where maximum infill genuinely helps. You enter the infill percentage and material type into the calculator below to estimate the relative strength and weight of a solid part versus a hollow one.

Formula

Weight = Part Volume × Material Density × (Infill % / 100)

Where:

• Part Volume (cm³) is the volume of the finished part as designed.
• Material Density (g/cm³) is the density of the filament (e.g., PLA ≈ 1.24 g/cm³, ABS ≈ 1.04 g/cm³, PETG ≈ 1.27 g/cm³).
• Infill % is the percentage of internal volume filled with plastic.

The strength factor is assumed to scale linearly with infill for simplicity, but real strength depends on layer adhesion, infill pattern, and loading direction.

Worked Example

Using the default values: volume = 100 cm³, density = 1.24 g/cm³ (PLA), infill = 100%.

1. Weight = 100 × 1.24 × (100/100) = 124 g
2. Solid weight = 100 × 1.24 = 124 g
3. Strength factor = 100%

The calculator shows 124 g for both weight and solid weight, confirming that 100% infill produces a fully solid part.

Background: Why Infill Matters

Infill is the internal lattice structure that gives a 3D printed part its shape without using excess material. Most prints use 15-30% infill for a balance of speed, weight, and strength. However, when a part must withstand crushing forces or sudden impacts, the internal structure becomes the limiting factor. At low infill, the walls and top layers carry the load, and the sparse interior collapses under pressure. 100% infill eliminates all voids, making the part essentially solid plastic. This dramatically increases compressive strength and impact resistance compared to hollow prints, though it also increases print time, material use, and cost.

How 100% Infill Affects Mechanical Properties

Fully dense parts behave differently under stress than partially filled ones. The main advantages are:

• Higher compressive strength: Solid plastic resists crushing better than any lattice.
• Better impact absorption: Without internal air gaps, cracks have no easy path to propagate.
• Improved surface quality on top layers: No infill pattern shows through, giving a smoother finish.
• Water and air tightness: Solid parts are less likely to leak.

However, 100% infill does not always mean the part is unbreakable. Layer adhesion is still a weak point; a solid part can still split along layer lines if the load is applied perpendicular to the layers. Also, warping and shrinkage can be worse in solid parts because there is more material to contract.

Five Practical Uses for 100% Infill

Here are five specific applications where 100% infill is the right choice:

1. Functional replacement parts under load: Gears, brackets, and hinges that must transfer force without deforming. For example, a gear in a low-speed mechanism needs solid teeth to avoid stripping.
2. Tools and fixtures: Clamps, vices, or jigs that are squeezed or hammered. A solid wrench or mallet head will survive repeated impacts.
3. Protective enclosures: Cases for electronics that might be dropped. A solid shell absorbs more shock than a hollow one.
4. Machined-part substitutes: When you need a part that will be drilled, tapped, or sanded, solid plastic provides better holding power for screws.
5. Pressure or vacuum components: Flanges, fittings, or chambers that must hold air or liquid without leaking through internal voids.

How to Choose Infill for Your Part

Selecting infill depends on the part’s role. Use this guide:

• 0-15%: Visual prototypes, display pieces, or parts that never see load.
• 15-40%: General-purpose parts, enclosures, and light mechanical use.
• 40-80%: Parts that need extra rigidity or will be exposed to moderate stress.
• 100%: Parts that must withstand crush loads, impacts, or high temperatures (since more plastic resists heat softening longer).

Also consider the infill pattern. For 100% infill, the pattern matters less because there are no gaps, but for lower infill, use gyroid or honeycomb for isotropic strength, or grid for faster printing.

Common Problems and Misconceptions

A frequent misconception is that 100% infill makes a part indestructible. In reality, it only improves strength in certain directions. Another issue is print time – a solid part can take 3-5 times longer than a 20% infill part. Warping is also more common, especially with ABS or nylon, because the solid mass cools unevenly. To mitigate this, use a heated bed, an enclosure, and consider printing with a smaller nozzle layer height for better adhesion.

Another problem is that slicers sometimes show 100% infill but still leave tiny gaps between walls and infill. Ensure your wall count is high enough (3-4 perimeters) so the interior is truly solid.

Cost and Material Considerations

Using 100% infill roughly doubles or triples material usage compared to typical prints. For a part that is 100 cm³, a 20% infill print uses about 20 cm³ of plastic, while 100% uses 100 cm³. That means higher cost and more waste if the part fails. Always test with a lower infill first if you are unsure, and only go solid when the part’s function demands it.

Material choice matters too. PLA is brittle and may crack on impact even when solid. ABS or PETG are tougher, and polycarbonate or nylon are even more impact-resistant. For extreme loads, consider metal parts instead of plastic.

Safety and Best Practices

When printing solid parts, be aware of increased heat buildup in the nozzle and part. Ensure your printer’s hotend can maintain temperature, and watch for clogging. Also, solid parts are heavier – make sure your printer’s build plate can handle the weight without shifting. When sanding or machining solid prints, wear a dust mask because plastic particles can be harmful to inhale.

Frequently Asked Questions

Does 100% infill make a part waterproof?

Generally yes, but not always. Small gaps between layers can still allow water to seep through. To guarantee watertightness, use more walls, increase extrusion width, or apply a coating like epoxy.

Is 100% infill stronger than a part with more walls?

Not necessarily. For bending and impact, increasing wall count (perimeters) often helps more than infill. A part with 5 walls and 50% infill can be stronger than a 2-wall part at 100% infill because walls carry most of the load.

What infill percentage is best for a phone case?

For a phone case, 100% infill is overkill. 20-40% with a flexible filament like TPU provides good shock absorption while staying lightweight. Solid TPU would be too heavy and stiff.

Can I use 100% infill with any filament?

Yes, but some materials are more prone to warping. ABS and nylon will shrink more, so use an enclosure. PLA is easiest but brittle. For impact parts, use PETG or polycarbonate.

How much longer does 100% infill take to print?

Print time scales almost linearly with material volume. A 20% infill part might take 2 hours; the same part at 100% could take 6-8 hours, depending on size and layer height.

Does 100% infill affect dimensional accuracy?

It can. More material means more shrinkage, especially in large parts. Expect slightly larger tolerances. To improve accuracy, calibrate your extrusion multiplier and print at a lower temperature.

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in infill | Infill % | % | 100 | 0
in density | Material density | g/cm³ | 1.24 | 0
in volume | Part volume | cm³ | 100 | 0
out weight | Part weight | g | volume * density * (infill / 100) | 1
out solid_weight | Weight if solid | g | volume * density | 1
out strength_factor | Strength vs solid | % | infill | 0